VAT headache !!

Haggis

Please would anyone be so kind and explain some probably quite simple facts about VAT that I seem to have got myself muddled with.
My client has a registration date for VAT as 1.7.05, however he did not start charging VAT on his invoices until 1.1.07. His previous accountant identified an amount owing on his balance sheet for yr ended 31.3.06 as £3924.
(He has not filled in any VAT returns for this period and has just been paying assessments)
My first question is how do I calculate the VAT owing for this period before 1.1.07 ? (when he started charging VAT)
(He is on the flat rate scheme and I am at present calculating his returns in the normal way)

many thanks, really appreciate your help.

Newbie

Assuming effective date of reg as 01.07.05 I would confirm FRS registration from this date with the client and also remember the 1% discount in first yr. FRS vat is calculated on gross turnover. Need to make a full disclosure to HMCE or consider disengaging etc