Are you a one man band or owner of your company?
The reason I ask is I am self employed and if a client gave me a cheque for £1000, me having given him some good assistance, I would regard that as fair and reasonable and would trouser it. I wouldn't think of it as a gift, more an ex-gratia to reflect the fact I'd saved the client a lot of money or whatever
However, if an employee gets something like that then it's quite a different matter