Ive been in this game over 14 years and I can honestly say Ive only had three debts in that time that I've had to write off.
Two were for negligible sums, maybe £10 each or so and the third was for £960 from a builder about 18 months ago. Still waiting for the receiver to sort their books out, I might get £1.50 from that after the banks and tax-man have their slice.