You appear to have submitted an incorrect tax return for 2010-11, in that you have included expenses from self employment (which are not allowable against your employment income) and which in any case relate to 2011-12. You need to file an amendment to your 2010-11 tax return.
You can't claim your van as an expense, but you can claim capital allowances. Yes, you can claim in 2011-12 even if the van was purchased in 2010-11.
Also, I incurred a number of parking fines and congestion charges during my first year because I had to wait 90 days for payment from my customers and sometimes didn't have the money to pay these - can I claim them as an expense of the business?
What does waiting for payment from customers have to do with incurring parking fines and congestion charges? You can claim congestion charges (just the charge, not any penalty) if the expense was incurred wholly and exclusively for the purposes of the business. In most cases parking fines are not allowable, but please state the precise circumstances in which they arose, why you incurred them and why you didn't or couldn't park legally.