Do the 2-4-6 changes mean that cheques are safer from fraud?
No, you should always be wary of accepting high-value cheques or bankers' drafts. If you don't know or trust the person offering you a cheque, you should consider other options such as a CHAPS payment, a telephone or internet payment or cash. Ask your bank for advice if you're in any doubt.
If your chequebook is stolen and used by a fraudster you will continue to enjoy full protection from financial loss - provided you haven't breached the terms and conditions of your account. You should report a loss or theft as soon as you notice it.