I don't follow this, perhaps you can explain.
How come new bikes need lights front and rear, but older bikes can get a daytime MOT only?
Aren't there any exceptions for new bikes with daytime only use?
Or are you stuck with lights for three years, then go for daytime MOT?
It's a real can of worms. I looked into it in great detail when I had a track bike (race fairings with no lights) as I wanted a daytime mot for that but after a lot of research and getting confirmation from serving Police Traffic Officers I did track days with I decided against it. Its also the reason I had the wiring kit fitted to my WR at new as I knew I'd get enough interest from the Police simply riding it on lanes/roads around here (Peaks).
In a nutshell ...
ANY bike manufactured after 1989 needs to comply with the Road Vehicle Construction and Use Regs 1986 - namely (here) the Vehicle Lighting Act 1989 (Amended 2005). This act stipulates what is required to ride on the roads legally from new and the key point is that bikes manufactured with front and rear facing lights must have them fitted and operational to be legal on the road.
The only motorbike exceptions to this rule are trial bikes (as in Dougie Lampkin style).
So, to be road legal you need to have front and rear facing lights if you use it on the road. This is for any motorbike, the only exception being trial bikes.
The MOT has no bearing on this as it only comes into play three years after new and is only a certificate to say the bike has met some tested criteria for one particular test one day a year.
In this threads case the MOT would become important if the OP bought the bike as it stands with hard wired lights. It will be fine for 3 years, but would then need a lights switch fitting (plus horn/reflector/numberplate light etc so basically a wiring kit) to pass the MOT.
The fact that some garages will issue daylight mots confuses things as technically they are not legal (unless you have a trial bike or an exempt vehicle such as Combat vehicle, incomplete vehicle proceeding to a works for completion etc).
Some garages (who issue daylight mot's) will refer to the grey area created by trials bikes exemption or may say its the MOT criteria thats important - where you only test whats there on the day of the mot. So no lights present = you can't test lights.
In this threads circumstances the OP would need to remove the lights from the bike to get a daylight MOT or completely obscure them. (Although obscuring/taping up would be to the discression of the MOT testing station as some will insist on testing anything physically on the bike).
To be fair to Garages/MOT Stations the onus is not on the garage issuing the MOT to bother whether the bike is road legal above and beyond it meeting the criteria of the MOT test.
I have quite a few mates that have ridden on daylight MOTs with no problems so despite the law the chances of getting prosecuted based on this nowadays are very slim. We don't generally have enough Police to worry about and your every day Policeman is unlikely to know this act well enough anyway. You would need to get stopped by a clued up Traffic Officer. It wasn't a chance I wanted to take as the Police are very keen around here on the roads and in the last 18 months on the (green) lanes aswell.
I've only personally heard of two people being done - One mate got stopped by a Policeman in Derbyshire who knew his cons & regs (no lights on bike/ daylight MOT) and got a fine and points iirc. The other was a guy riding a sports bike with no lights/ daylight MOT. He was involved in an accident with a fatality (not him) which a friend (a serving Traffic Officer) attended. His insurance were arguing against his claim as they said the bike was not road legal and he had not informed them of it being modified from original spec.
Like I said - Proper can of worms!