Image copyright PAcemaker Image caption DUP leader Peter Robinson on board one of the buses during his party's manifesto launch

The public body that operates London transport has said it was unaware one of its iconic Routemaster buses was to be used in a DUP election event.

The party used a double-decker at its manifesto launch as a backdrop to speeches and photo opportunities.

Media interviews were conducted on a second bus.

Transport for London (TfL) said had it been asked, it "would not have given permission for the bus to be used given pre-election rules for public bodies".

The DUP staged the event in Antrim, at one of the factories belonging to Wrightbus, the company that builds the buses for TfL.

The design copyright for the Routemaster, sometime dubbed the Boris Bus after the London mayor, is owned by TfL.

Rules ban tax payer funded resources being used for election campaigning purposes.

The TfL statement added: "We are very proud of our association with Wrightbus and the work we do with them in Northern Ireland and look forward to future collaborations with them."

The company is headquartered in Ballymena and its founder William Wright, 87, was one of those who signed the nomination papers of incumbent DUP MP and candidate in North Antrim, Ian Paisley.

Wrightbus has declined to comment on the use of the bus by the DUP.

SDLP MLA John Dallat said the DUP "know full well the rules of the [election campaign] game".

He said: "This latest incident demonstrates an arrogance and complete contempt for the rules on behalf of the DUP.

"They must make explicit whether they paid for the use of Wrightbus premises or if this will be considered a donation to their campaign."