Conservative members of Brighton and Hove City council’s planning committee have admitted ignoring national conduct guidelines.

The admission, made at a meeting on Thursday, followed just days after the councillors were criticised for voting not to order a developer to make a £145,000 community contribution a week after he had donated £2,000 to their party’s coffers.

Conservatives said they had done nothing untoward and insisted all planning decisions were taken fairly.

The party’s leader, Mary Mears, confirmed Tory members of the planning committee gathered in private prior to planning meetings.

The confirmation, which came amid a debate over sandwiches being supplied to councillors for meetings, was greeted with outrage by opposition parties.

Labour and Green councillors pointed out that guidelines issued by the Royal Town Planning Institute, and followed by many councils, discouraged any party from having premeetings on the basis they could be used by members to predetermine how they would vote on the planning applications due to be decided.

Yesterday, Councillor Lynda Hyde, chairwoman of the 12-member planning committee, and one of six Conservatives, said: “We do have informal meetings but I can state categorically that we do not hold discussions about how we will vote.”

She said she believed the issue was being used by the rival parties in an attempt to score political points ahead of the crucial by-election in the Goldsmid ward in Hove on Thursday.

The council is currently investigating a complaint made by Labour planning committee member Les Hamilton regarding a decision made in February.

He raised concerns that Conservatives, with the exception of Dawn Barnett, had voted to reject council officers’ recommendations that City Gateway Developments should contribute £145,000 towards public transport and art as part of permission to transform a disused warehouse in Wellington Road, Portslade, to a performing arts school and leisure centre.

Councillor Hamilton said he was concerned the firm’s director, Fash Ghiaci, had made a £2,000 donation to the Hove Conservative Association five days earlier which members did not declare as a prejudicial interest.

No evidence has been produced to show the payment had influenced the outcome but Coun Hamilton demanded transparency in all councillors’ dealings.

All those involved have stated the donation was not related to the planning application.

Green Party convener Bill Randall urged Hove Conservatives to donate £2,000 to charity to reassure the public it had arrived as an “unhappy coincidence”.

Heather Newberry-Martin, agent for the Brighton Pavilion and Hove and Portslade Conservatives, said: “The donation to campaigning is to rid this country of this appalling Labour Government by electing a Conservative Member of Parliament and has nothing to do with council issues whatsoever. Funding is for Parliamentary campaigns."

A council spokesman said: “The law states that committee members must not do anything to pre-determine applications or to appear to do so.