Worksheet 1: "Invoices" - shows Amount of invoice, VAT due, e.g.
£100.00 £17.50 £117.50
£200.00 £35.00 £235.00 etc
for all invoices, December, January, February (sub-total for each month
shown at end of 3 columns)

Worksheet 2: "Purchases" - identical layout as above.

Worksheet 3: "Summary"
This shows:
December Sales
January Sales
February Sales

VAT on sales
December
January
February

Continues same as above for Purchases.

I know that I can copy and paste the sub-totals from worksheets Invoices and
Purchases for each month onto the Summary worksheet but is there formula I
can use to do this automatically and show how much is due at the end of the
quarter, i.e. amount of VAT received, less amount of VAT paid out.

Thanks