You won't find a more realistic GBBR AR15 than the GHK unless you go Vipertech/Inokatsu which are pretty niche and you probably won't find anyone selling them in the UK unless you find a second hand one. Plus they're based on the ancient WA system which GHK is an updated version of.
The TM MWS is a great airsoft gun but it's not a very good imitation of a RS gun.
It seems your options out of the box that requires no mods are the GHK MK16 URG-I/MK16/M4 keymod or a TM MTR16/MK16.
At the end of the day, you'll be happy with the TM or the GHK. The TM is more performance orientated so would be more suitable for skirmishing. The GHK, more realistic, better RS parts compatibility. Plus, you can set it up to run CO2 for that extra specialness.
Wildcard, there are the Rare Arms guns which are a bit pricey but very cool. Especially if it's just going to be used for training at home where picking up the shells won't be so much of a PITA.
https://www.crw-airsoft.com/rare-arms-m4-145-r-system-co2-gbb--shell-ejecting-13750-p.asp