London Marathon actually has an official partnership with Guinness Records to give out world records at the race for joke runs:
Seventy-three Guinness World Records attempts in 2017
11/04/2017
Guinness World Recordsâ„¢ has collaborated with the Virgin Money London Marathon for the tenth consecutive year to provide the most creative and determined fun runners with on-the-Finish-Line world record verification.
A huge 73 world records are being attempted this year, featuring a total of 86 runners, and a team of Guinness World Records adjudicators will be on hand to check costumes, verify times and confirm successful runners as official GWR title holders, earning them a place in the 2018 book out in September.
And in the London Marathon 2017 these runners set their joke world record runs:
There were 37 new Guinness World Records at the marathon, title holders are listed below:
1. Joe Spraggins, Fastest marathon dressed as a swimmer – 2:42:24
2. Ashley Payne, Fastest marathon dressed as an elf – 2:58.:26
3. Gary McNamara, Fastest marathon dressed as a fast food item – 2:59:35
4. Paul Richards, Fastest Marathon dressed as a Viking – 3:03:16
5. Malcom Treby, Fastest marathon dressed as a monk – 3:03:31
6. Evan Williams, Graham O’Loughlin and Ian Williams, Fastest marathon in a three person costume (Fish in the sea) – 3:13:09
7. Simon Couchman, Fastest marathon dressed as a crustacean – 3:13:18
8. Rebecca Cesar de Sa, Fastest marathon in film character costume (female) – 3:16:19 (Wonder Woman)
9. Laurence Morgan, Fastest marathon in a full-body animal costume – 3:16:27
10. Daniel Jordan, Fastest marathon dressed as a nun – 3:17:12
11. Damian Thacker, Fastest marathon wearing wellington boots – 3:21:27
12. Max Livingstone – Learmonth, Fastest marathon dressed as a Bishop – 3:21:32
13. Sarah Dudgeon, Fastest marathon dressed as a monk (female) – 3:21:33
14. Terry Midgley, Fastest marathon dressed as a chef – 3:22:27
15. Philip Powell, Fastest marathon dressed as a Mr. Potato Head – 3:24:19
16. Rebecca Vincent, Fastest marathon dressed as a cartoon character (female) – 3:24:28 (Mini Mouse)
17. Nicola Nuttall, Fastest marathon dressed as a witch (female) – 3:26:13
18. Victoria Carter, Fastest marathon dressed as a nun (female) – 3:26:53
19. Kevin Day, Fastest marathon dressed as a French Maid – 3:26:43
20. Alex Smith and Chris Stone – Fastest Marathon in a two-person costume (Jamaican Bobsled) – 3:33:22
21. Lorna Pursglove, Fastest marathon dressed as a fruit (female) (Chilli Pepper) – 3:41:25
22.David Smith, Fastest marathon in a sleeping bag – 3:44:01
23. Julia Mitchelmore, Fastest marathon dressed as a cheerleader (female) – 3:46:55
24.Cat Dascendis, Fastest marathon female dressed as a gingerbread girl – 3:46:55
25. Mark Conlin, Fastest marathon dressed as a medical instrument (Insulin pump) – 3:48:09
26. Gemma Stevens, Fastest marathon dressed in a full body dinosaur outfit (female) – 3:57:46
27. Kou Tseng, Fastest marathon dressed as a padlock – 3:59:40
28. Warren Edwicker, Fastest marathon dressed as a telephone box – 4:07:57
29. Alice Gerlach, Fastest marathon dressed as a television character (female) – 4:13:39 (Banana Man)
30. Michael Law, Fastest marathon dressed as a star – 4:20:07
31. Jayne Moreton, Fastest marathon dressed as a dragon (female) – 4:32:54
32. Tom Langdown, Fastest marathon wearing chainmail (upper body) – 4:50:16
33. Susan Ridgeon, Fastest Marathon in a Toilet Roll Costume (Female) – 4:54:00
34. Thomas Bolton, Fastest marathon dressed as a car (Del Boy’s Yellow Robin Reliant) – 4:55:.09
35. Jeremy Allinson, Fastest marathon dressed as a Star Wars character (Storm Trooper) – 4:59:12
36. Paul Cousins, Fastest marathon dressed as a three dimensional aircraft (Helicopter) – 5:03:15
37. Ben Blowes, Fastest marathon carrying a household appliance (white goods – Tumble drier) – 5:58:37
38. David Hepburn, Meg Walker, Ceyhun Jay Uzun, Andy Sharpe & Holly Bishop, Fastest marathon in a five-person costume (Scooby Doo’s Mystery Machine) – 6:17:26
39. Marc Jenner, Fastest marathon carrying a 100 lb pack – 6:47:03