Steve,
You will be charged with two motoring offences in this case. The first one will be
driving without licence as you did not have a valid licence (provisional licence holders must be accompanied by someone over 21 and having 3+ driving experience) and the second offence relates to
driving without insurance (note that not having a valid licence would invalidate any insurance you may have anyway).
For the first offence, there's a penalty of 3-6 points on your licence and a fine of upto £1000.
For the second offence, there's a penalty of 6-8 points on your licence and a fine of upto £5000.
You may as a result be banned from driving as well but since this is your first offence, I doubt you will have prison sentence unless you don't pay up your fines.