Bookkeeping - can I withhold records until I am paid

 I am a self employed bookkeeper and one of my long term clients has recently informed me that he has changed his accountants and that they will also be doing his bookkeeping from now on.  We have had a relaxed working relationship whereby, because I knew of his cash flow problems, I did not chase my money and he would pay lump sums when he could.  Unfortunately he now owes me just under £2k and I am very reluctant to release anything to his new accountants until I have been paid in full.

I have already drafted out a letter thinking that I have a right to do this, but now I am unsure if legally I have to hand anything over to them straight away.  I have in my office a complete years worth of invoices, bills etc., PAYE records and I work on my own copy of QuickBooks to do his accounts.  The accountants are asking for all this plus a backup of QB.  I have stated that I would hand over the PAYE records now in order for them to continue with the employee wages.

I have seen from his cheque book that my client has post-dated some very large cheques to HMR&C so I can't see him being able to pay me any time soon, but I am afraid that if I hand over everything he will just bluster and may even stop trading (he trades as self-employed).

Can anyone advise my best course of action?  I don't want to go in heavy handed so I thought I would suggest that he sets up a monthly standing order.  If he did this and then reneged on the payments would I have a better  chance of taking him through the courts?

I feel that I am having to walk on tender-foot as I don't want to put his back up by making him feel that I can't trust him, but on the other hand I have been taken for a ride by other "nice" clients in the past!

Thank you for you time