Armed Police were denied entry to Westgate prison after they arrived to assist with a drugs swoop.

An "amicable'' confrontation between Emergency Response Team members and Prison officials occurred outside the building after concerns that the ERT's presence could incite trouble within the prison.

After a stand-off for 20 minutes, the ERT stayed outside while plain-clothed officers conducted a partial search of administration areas of Westgate.

It is understood Prison officials supported the drugs raid but became concerned when armed officers wearing bullet proof vests arrived.

There were unsubstantiated claims that the reason ERT were present was because of fears that a gun may have been inside one area of the prison.

The incident came days after the 1999 Treatment of Offenders Board report highlighted drugs as a "very serious problem'' in the facility, adding that the use of sniffer dogs once a year was inadequate.

Nothing was apparently found after the search -- carried out with sniffer dogs -- which lasted about 30 minutes and included areas housing prison officers' lockers.

An unnamed prison officer last night said the situation had arisen because of "miscommunication'' between the two agencies.

"It was initially a joint effort but they weren't allowed in with ERT, with the equipment they had it may have created a problem if they did come in fully equipped,'' he said.

"It may have incited something, there was no problem with them doing the search.'' It is understood that ERT officers waited outside while ten other officers did a limited search inside. No cells were inspected.

Last night a Police spokesman confirmed officers were at Westgate to conduct searches but refused to comment on claims that there had been a confrontation outside.

He said: "We can confirm police were at Westgate, gained entry to the facility and conducted searches.

"We will be liaising with prison management with regard to future investigations of breaches of the misuse of drugs act and prison rules.'' Prison Officers Association chairman Michael Tuzo said the failed operation hadn't upset his members.

He said they welcomed drugs search but called for a more unified approach to dealing with the issue.

"If we are going to make a concerted effort to rid the drugs problem, all agencies have to sit down and really think it out, it is a very serious problem, he said.

"We do welcome the effort but we need to do it together, a concerted effort to tackle the problem.'' It has been acknowledged that it is very difficult to keep drugs out of prison and the 1999 Treatment of Offenders Report said drug use and trafficking were a serious problem.

It called for more drug testing of inmates and last Friday Labour and Home Affairs Minister Paula Cox gave permission for increased random inspections using dogs.