I use these...
http://www.ebay.co.uk/itm/350360387159?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
I've used LED tail lights with built in indicators on Streetfighter projects before. My GPZ1100 had a ZX636 seat unit with after market lights. The only issue was having to put inline resistors in place so the indicators flashed at the correct frequency.
The modern ultra-bright LED tail lights are within the bounds of the construction and use regulations but as far as M.O.T testers go you'll either get...
"If they work they're fine".
...or...
"Sorry you need lights in keeping with the age of the vehicle".
Ask your local M.O.T guys before spending your money.