The UK's Secretary of State for Exiting the EU, David Davis, has refused to hit back at his former chief-of-staff after he made a series of allegations against the senior Conservative.

James Chapman, the ex-political editor of The Daily Mail and former aide to George Osborne, claimed that Davis had Eurosceptic firebrand Nigel Farage "on speed dial" and only worked a three-day week.

Chapman, who is organising a pro-EU demonstration in Westminster's Parliament Square in September, also said that he witnessed Davis being "drunk, bullying and inappropriate" to Labour's Shadow Home Secretary Diane Abbott.

Davis later denied that he had Farage on "speed dial", but confirmed that he had the former Ukip leader's number.

He also told Sky News: "James was a 'Remainer' from the beginning, but he was a very good chief-of-staff. I am not going to criticise or argue with him."

Chapman, a partner at City PR firm Bell Pottinger, is planning to set up a new centrist political party called the Democrats.

The married father-of-two's intervention comes at the early stages of the two-year-long Brexit negotiations between the UK and Brussels, with French politician Michel Barnier leading the talks for the EU.

The British government announced on Tuesday that it will seek a transitional deal with the EU so that the UK can stay in the bloc's customs union for up to three years after Brexit in 2019.

The decision is controversial among Eurosceptics since since staying in the customs union would prevent the UK brokering its own free trade deals with non-EU nations.