Client doesn't know if it's on CASH or STANDARD VAT scheme

HMRC won't know which method they're using as there's no requirement to tell them. It may be recorded in an inspector's file if they've had a VAT inspection but I doubt the call centre staff will have access to that. If you cannot contact the previous accountant I would suggest putting together a list of the VAT included on debtors and creditors opening balances on the first date which you're preparing returns from. If there's no material difference between the two then it's not going to make much difference which scheme you choose to use - if there is a big difference then try to reconstruct the previous quarter's return and making a guess which scheme was used based on what looks closest to the figures filed.

Jodie