They did not allow me
My wife had her FP notice and I did not get it. I tried to request them at Manchester to take my FP as well. They did not entertain my request. But you can try your luck, just don't be too hopeful and feel bad later. You have nothing to lose by trying.
If you have a FP notice and then you are trying to go early, I would suggest that you go on a day other than wednesday. Wednesday is the day when they accept people who have missed their appointments and it is generally more people on that day. Also, try going there at around 11.00 AM instead of early morning if possible. Usually there is a lady at the FP counter and she does not really care if you go early. But if you find that spanish guy at the window, then expect some rude behaviour.
Hope this helps