The UK’s chief negotiator has warned “we may not succeed” in securing a Brexit trade deal as he made a surprise arrival in Brussels for renewed talks. Lord Frost signalled that he would not be deviating from Boris Johnson’s “red lines” amid speculation that the departure of Dominic Cummings from No 10 could herald concessions. He said there had been “some progress in a positive direction” but admitted there were still “significant” differences between the UK and EU on fishing and the level playing field. His tone was echoed by Simon Coveney, the Irish Foreign Minister, who said a deal was “very doable” but also “very difficult” and could be scuppered by deadlock over fishing, with the EU demanding 50 per cent of the catch in British waters and the UK sticking at 20 per cent. Mr Coveney also repeated the EU’s warning that it would not ratify any deal unless clauses in the Internal Market Bill overriding the Brexit divorce terms were dropped, although he also suggested that issue will “disappear” if there is a wider trade deal.