I've compiled a list of UK ultramarathons, ordered by distance. There may be innacuracies, mistakes and races missing. Please let me know if you spot any of them.

trail 3 Forts Marathon
http://www.threefortsmarathon.org.uk
Distance: 27.0 miles (43.5km)
Ascent: 3,450 ft
Time limit: 6h
Best time: 03:07:03
Usual date: May
trail Downland Ultra Challenge
http://www.haywardsheathharriers.co.uk/nonMembers/...
Distance: 30.0 miles (48.3km)
Usual date: July
trail The JW Ultra
http://www.ultrarunner.co.uk/index.php?option=com_...
Distance: 30.0 miles (48.3km)
Usual date: September
trail Wuthering Hike - Haworth Hobble
http://www.kcac.co.uk/?page_id=199
Distance: 31.0 miles (49.9km)
Ascent: 4,400 ft
Best time: 03:43:24
Usual date: March
road Fife AC 50K
http://bcruickshank.brinkster.net/page6.htm
Distance: 31.06855961 miles (50.0km)
Best time: 03:02:27 ?
Usual date: May
exceptionnally in September this year
road Boddington 50K
http://www.glosaaa.org.uk/images/Bodd_50k_2007_EF....
Distance: 31.06855961 miles (50.0km)
Usual date: August
trail Manx Mountain Marathon
http://www.manxfellrunners.co.uk/manxmntnmarathon/...
Distance: 31.5 miles (50.7km)
Ascent: 8,000 ft
Best time: 04:22:45
Usual date: April
road Dartmoor Discovery
http://www.hmca.org.uk/marathon/
Distance: 32.0 miles (51.5km)
Usual date: June
trail Marlborough Downs Challenge
http://www.marlboroughrunningclub.co.uk/downchalle...
Distance: 33.0 miles (53.1km)
Best time: 4:06:28
Usual date: May
trail Osmotherley Phoenix
http://www.runfurther.com/index.php?option=com_con...
Distance: 33.0 miles (53.1km)
Ascent: 4,000 ft
Usual date: July
trail Calderdale Hike
http://www.sowerby-bridge.org.uk/scouts/chike/inde...
Distance: 34.0 miles (54.7km)
Usual date: April
road Draycote Water 35
http://www.krrac.info/DW_Info.asp
Distance: 35.0 miles (56.3km)
Best time: 03:42:22
Usual date: February
loop Barry 40 mile track race
http://www.lescroupiersrunningclub.org.uk/barry40/
Distance: 40.0 miles (64.4km)
Time limit: 6h
Best time: 04:08:16
Usual date: March
trail High Peak 40
http://www.highpeak40.co.uk
Distance: 40.0 miles (64.4km)
Best time: 05.31.08 ?
Usual date: September
trail High Peak Marathon
http://www.highpeakclub.union.shef.ac.uk/hpm/
Distance: 40.0 miles (64.4km)
Best time: 09:21:56 ?
Usual date: March
trail Tring 2 Town
http://www.ambitionevents.com/tring2town/
Distance: 40.0 miles (64.4km)
Best time: 05:19:00
Usual date: February
trail Compton Downland Challenge 40 miles (Full Fat Forty)
http://comptonharriers.cjb.net
Distance: 40.0 miles (64.4km)
Ascent: 3,900 feet
Usual date: March
Not this year
trail Lyke Wake
http://www.lykewakewalk.co.uk/
Distance: 42.0 miles (67.6km)
Usual date: July
trail Across Wales 42 miles
http://www.newtown-rotary.org.uk
Distance: 42.0 miles (67.6km)
Usual date: June
not to be confused with the "Across Wales Walk"
trail Devil O' The Highlands
http://devilothehighlandsfootrace.co.uk/
Distance: 43.0 miles (69.2km)
Time limit: 12h
Usual date: August
trail Rhayader Mountain Trail
http://www.runfurther.com/index.php?option=com_con...
Distance: 43.0 miles (69.2km)
Usual date: August
trail Across Wales Walk
http://www.whereitsat.pwp.blueyonder.co.uk/AWW/Ind...
Distance: 45.0 miles (72.4km)
Time limit: 18h
Best time: 08:08:00
Usual date: September
not to be confused with the "Across Wales 42 miles"
trail The Four Inns Walk
http://www.dynarx.demon.co.uk/fourinns/index.html
Distance: 45.0 miles (72.4km)
Best time: 07:19:00
Usual date: April
trail Afoot in Two Dales
http://www.ldwa.org.uk/news/news_story.php?menu=Y&...
Distance: 50.0 miles (80.5km)
Ascent: 5,800 ft
Usual date: July
road John Lucas Memorial Run
http://www.strathavenstriders.co.uk/
Distance: 50.0 miles (80.5km)
Usual date: August
trail The Longmynd Hike
http://www.longmyndhike.org.uk
Distance: 50.0 miles (80.5km)
Ascent: 8,000 ft
Time limit: 24h
Best time: 08:03:00
Usual date: October
trail Rowbotham’s Round Rotherham
http://www.hmarston.pwp.blueyonder.co.uk/rhac/trai...
Distance: 50.0 miles (80.5km)
Best time: 06:17:50
Usual date: December
trail The Thames Path Ultra
http://www.ambitionevents.com/thamespathultra
Distance: 50.0 miles (80.5km)
Time limit: 16h ?
Best time: 06:18:30
Usual date: January
trail Durham Dales Challenge
http://www.walknortheast.org.uk/ddc2007.html
Distance: 52.0 miles (83.7km)
Best time: 10:57:00
Usual date: June
also a 28 miles
trail 50 Mile Challenge
http://www.50milechallenge.co.uk/2.html
Distance: 52.4 miles (84.3km)
Time limit: 15h
Usual date: July
trail The Night Day Marathon
http://www.ambitionevents.com/nightday
Distance: 52.4 miles (84.3km)
Time limit: 24h
Usual date: July
Also in August
trail The Original Mountain Marathon (was "Karrimor Mountain Marathon")
http://www.theomm.com
Distance: 52.4 miles (84.3km)
Ascent: 3,000m
multiday - 2 days
Usual date: August
trail Highland Fling
http://www.highlandflingrun.co.uk/
Distance: 53.0 miles (85.3km)
Time limit: 15h
Best time: 07:26:15
Usual date: May
trail Thames Meander
http://www.thamesmeander.com
Distance: 54.0 miles (86.9km)
Time limit: 18h30
Best time: 07:55:00
Usual date: February
road London to Brighton
http://www.roadrunnersclub.org.uk/?q=londontobrigh...
Distance: 55.0 miles (88.5km)
Usual date: October
defunct
trail Bullock Smithy Hike
http://www.bullocksmithy.com/
Distance: 56.0 miles (90.1km)
Best time: 08:55:00
Usual date: September
trail Fellsman
http://www.fellsman.org.uk
Distance: 60.0 miles (96.6km)
Ascent: 11,000 ft
Best time: 10:15:00
Usual date: May
trail Surrey Summits Marshal's Walk
http://ourworld.compuserve.com/homepages/RegChapma...
Distance: 62.0 miles (99.8km)
Usual date: April
road Self Transcendence 100k
http://www.srichinmoyraces.org/uk/ultras/selftrans...
Distance: 62.137119224 miles (100.0km)
Best time: 07:04:46 ?
Usual date: May
road Gloucester 100k
http://www.runnersworld.co.uk/events/viewevent.asp...
Distance: 62.137119224 miles (100.0km)
Not sure it's still being held
trail Bob Graham Round
http://www.bobgrahamround.co.uk
Distance: 74.0 miles (119.1km)
Ascent: 28,500 ft
Best time: 13:53:00
can be attempted ay time ?
trail Ridgeway Challenge
http://www.tra-uk.org/ridgeway_challenge.php
Distance: 85.0 miles (136.8km)
Ascent: 9,000 ft
Best time: 15:18:00
Usual date: August
trail West Highland Way Race
http://www.westhighlandwayrace.org
Distance: 95.0 miles (152.9km)
Ascent: 14,760 ft
Time limit: 35h
Best time: 15:44:50
Usual date: June
trail Pennine Relentless Challenge
http://www.ambitionevents.com/penninechallenge/
Distance: 100.0 miles (160.9km)
Ascent: 10,000m
Best time: 27:07:00
Usual date: June
trail Northumberland 100
http://www.runnersworld.co.uk/events/viewevent.asp...
Distance: 100.0 miles (160.9km)
Usual date: May
Not sure it's still held
trail Lakeland 100 (Ultra Tour of the Lake District)
http://www.lakeland100.com
Distance: 100.0 miles (160.9km)
Ascent: 6,300m
Time limit: 40h
Usual date: August
first edition in 2008 - also a 50 miles
trail Marathon of Britain Coast
http://www.ambitionevents.com/mobcoast/
Distance: 103.0 miles (165.8km)
Ascent: 10,000m
Usual date: July
trail Hardmoors 110
http://www.hardmoors110.co.uk
Distance: 110.0 miles (177.0km)
Ascent: 6,000 m
Time limit: 36h
Usual date: September
first edition in 2008
trail Grand Union Canal Race
http://www.gucr.co.uk
Distance: 145.0 miles (233.4km)
Time limit: 45h
Best time: 27:35:00
Usual date: May
trail Marathon of Britain
http://www.ambitionevents.com/mob/
Distance: 175.0 miles (281.6km)
Usual date: September
trail Seni Extreme 200
http://www.ambitionevents.com/seniextreme
Distance: 200.0 miles (321.9km)
Usual date: May
trail Green Belt Relay
http://www.greenbeltrelay.org.uk/
Distance: 220.0 miles (354.1km)
Best time: 21:10:15
Usual date: May
relay
loop St Catherines 6/12 hour Race (Crawley)
Time limit: 6/12h
Usual date: March
loop Hull 24 hour
http://www.webnet.karoo.net/24hr/24hrpage.htm
Time limit: 24h
Best distance: 141 miles
Usual date: July
loop Self Transcendence 24 hour
http://www.srichinmoyraces.org/uk/ultras/24hr06/
Time limit: 24h
Best distance: 143 miles
Usual date: October

Last update: Mon Apr 28 17:04:16 2008
55 ultras


Related links:
Ultramarathon list.