The organisation says no customer should have to queue for more than five minutes, but most have to.

It is calling for action from the Post Office after an investigation of 11 branches found in most there were not enough counters open to meet demand.

The Post Office acknowledged there were problems in some branches and that queuing times needed to be cut.

Longest queuing times (average in brackets) Bedford 6 minutes (average wait 1.5 minutes) Bletchley 15 minutes (8 minutes) Cambridge 21 minutes (10 minutes) Chelmsford 20 minutes (11 minutes) Colchester 6 minutes (3.5 minutes) Hertford 11 minutes (8 minutes) Ipswich Tower Ramparts 8 minutes (4 minutes) Luton Arndale 11 minutes (7 minutes) Norwich Castle Mall 8 minutes (6 minutes) Peterborough 10 minutes (7 minutes) Stevenage 19 minutes (7 minutes)

The Postwatch carried out two queue tests at each of the 11 branches after complaints from the general public.

The average queuing time at the Tower Ramparts branch in Ipswich was four minutes, at Castle Mall in Norwich it was six, and in Stevenage seven.

In Cambridge, the average was 10 minutes but some customers endured a marathon 21-minute wait before being served.

Dr Charles Winstanley, regional chairman of Postwatch, said: "Some post office transactions require additional time, and customers need to feel that they are not being rushed unduly just to keep queues down.

"Postwatch intends to continue monitoring service, including queues at thse and other branches within our region."

The Post Office spokesman said: "We aim to serve 95% of people within around five minutes but this is not the only aspect of customer service or satisfaction.

"It's no good serving people quickly if they receive poor service."

Postwatch is planning another undercover queue survey later this summer.