MOT guidelines for testign are here
http://www.transportoffice.gov.uk/crt/doitonline/bl/mottestingmanualsandguides/mottestingmanualsandguides.htm I cant post the direct link but click through to the correct vehicel class then the section on lighting
This inspection applies to: all vehicles, except those which either have no front or rear position lamps or have such lamps permanently disconnected, painted over or masked that are a. only used during daylight hours, and b. not used at times of seriously reduced visibility If this situation occurs, the vehicle presenter should be issued with a VT32 (advisory notice) recording the aboveSo basically a "daylight MOT appears to be a normal MOT with an advisory" Note id expect the vehicle to need to have clearley disconnect/obsured lights so a road car with a baby seat it and gaffer tape over the lights would likley be told to sling its hook by a tester. A kitted out trialer would more than likley get a fair test.
Daylight is defined in highway code here
http://www.direct.gov.uk/en/TravelAndTransport/Highwaycode/DG_070302Obviously you need to think about why you would do this and if you are sure its a valid reason. If its for a competition vehicle then check the class regs re lighting as its not just a case of MOT is all you need (my Sprint and Hillclimb car needs a heater fitted as its factory spec etc, even though thats not an MOT issue for example).
If you live 3 miles form a pay and play site and just want to drive there thats possibly sensible, but anything else could be troublesome, especially if you get stuck with a breakdown and its starts getting dark.