Niece got a very average score first time around. Just over 600 using the 600 question book. Second time around she purchased an online pack. Over 3000 questions (or similar)
and went up to a score of 750!
It seems familiarisation helps a lot. Also, the way it is done - online - needs some familiarisation. My niece said the online calculator took getting used to.
She's in the Far East but I'll try and find out what online pack she used and let you know. It was a month's crash course online
that she used.
Also, select very carefully the unis based on GCSE's, UKAT, PS, etc. They all have their own 'degrees of importance' depending which university to you apply to. Can't stress this aspect enough. Choose wisely which to apply to.