Possibly is the right answer.
I've got one fitted from Tuner-X and though they claim it's legal, it's not.
My local mechanics/MOT centre summed up the situation.
If the tail lights go out at any time when the indicator is flashing, it's illegal.
So, if you can find one which has a constantly illuminated tail, you're fine.
I'd already got mine before I found out but I guess you could write and ask before purchasing.
Personally, I don't care and when I got pulled recently, they told me my number plate was too small and weren't bothered about the rest.
You won't need an MOT yet so make sure you can find a sympathetic mechanics, like mine, when you do.