When I do my self assessment I work out all the figures inclusive of VAT as if I was not registered for VAT. (Yes people will probably bash me for this)
can I then put an expense on my self assessment for the VAT I have paid HMRC for that tax year?
Yes you can and should claim overall due vat as an expense - i am presuming sales are inclusive of vat charged so they will be higher than would be the case if you charged same net sum (excl vat) without being vat registered.
hmrc specific advise is as follows
https://www.gov.uk/government/uploads/s ... s-2015.pdf
If you include VAT, either:
• put your net VAT payment to us as an expense
in box 30, or
• put any net repayment you received from us in box 16.
If either payment includes VAT on capital items, you need
to give us the details in box 103 ‘Any other information’.
Include the VAT that is not recoverable when you work
out the capital allowances due on these items
(boxes 49 to 59).
Note it is very easy to get inconsistent results when you use this method eg with timing issues in relation to when vat is paid - for that reason i would never recommend using this method if possible - as you work out the vat due in the first place i would recommend swapping to doing everything net of vat (where vat has been accounted for or claimed back) - if you are on flat rate it is somewhat more complicated you would use gross vat inclusive sales less flat rate vat accounted for on those sales and expenses including vat where no vat has been reclaimed or net of vat if vat had been reclaimed (eg assets and pre-vat services)