Hi Louise and thanks for your reply.
I emailed Sykes twice asking specifically about the VAT on the actual bookings and twice they have come back with info on the VAT they charge on their commission despite me saying in my emails that was not what I was asking them. So I phoned them and to be honest, the person I spoke to didn't really seem to undertand what I was asking but did try her best to get some answers and was very pleasant.
So I phoned HMRC and then found this https://www.gov.uk/guidance/vat-instalments-deposits-credit-sales
So, I think the best way to do it is to account for the VAT on the deposit in the period that the deposit is received. So, say 17/04, £120 is received as a deposit then £100 net and £20 as sales VAT. Then when the balance is received that is put through in that period with the relevant VAT. If, in the event there is a cancellation and monies are due back at some point, then an adjustment would need to be made in that VAT quarter to reclaim the VAT
Does anyone agree? Or should it be done differently? Thanks!!