Prince Charles said the campaigners "might see sense prevail".

Conwy Council has approved its �11m plans for two extensions to its seafront theatre and conference centre, extending nine metres nearer the sea.

Supporters said it will provide a major economic boost for the town.

But critics have described the planned buildings as "monstrous" and totally unsuited to the conservation area.

The development plans include a new 2,000 square metre exhibition hall and arena, new syndicate rooms equipped with video conferencing and a business centre for delegates.

The local authority has already demolished the former Arcadia Theatre in preparation for building the arena.

But campaigners against the development said they have now enlisted the tacit support of Prince Charles in their opposition to the scheme.

Llandudno Civic Trust wrote to Prince Charles to ask for his backing

In his reply, the prince said he could not become involved in a local planning issue but said he was "saddened to read of the proposals" and that the campaigners' efforts "might see sense prevail".

'Create jobs and wealth'

John Lawson Reay, of Llandudno Civic Trust, said: "The design of the building belongs to the scope of the 1960s factory units.

"It's a monstrous development, which is totally alien and, apart from that, it protrudes about nine metres beyond the historic building line, which is totally unacceptable.

Peter Caldwell, of Mostyn Estates, which owns much of the town and has fought to retain its character, said the decision to go beyond the traditional building line could pose problems for the council later.

He said: "It means that a lot of hotel owners in adjoining properties will say 'wouldn't it be nice to build a big terrace on the front of our property?' How are we going to resist that?"

But Conwy councillor, Ronnie Hughes, said: "At the end of the day, is it for the benefit of people who look at the building, or is it to benefit the economics of the authority?

"As far as I'm concerned, as a Labour member, it's for the benefit of the people that I represent, to get jobs and to create wealth for this authority."

Work is due to start on the building early next year.