I just realised that I forgot to enter a whole bunch of expenses because I did it in a rush which will have affected my last VAT return.

How do I correct it? i.e. put in old charges now but have those accounted for in my next return which is due soon?

See this link

http://www.solaraccounts.co.uk/forum/topic.php?TopicId=413&Posts=1

Hi John,

You should enter the expenses dated in your previous VAT period, but Solar Accounts is not clever enough to add the VAT from those expenses to your next VAT return. The simplest approach is to manually calculate the VAT on those expenses and add it to Box 4 when you copy the figures from Solar Accounts to your VAT return.

Alternatively you can calculate the figures on your next return by setting a period of 6 months and subtracting your previous return - see this page for details:
http://www.solaraccounts.co.uk/forum/topic.php?TopicId=413&Posts=1

Regards,