Labour has called for an inquiry into allegations that Boris Johnson broke the ministerial code by using a taxpayer-funded plane for a byelection campaign visit. The claim was prompted by a report saying the Conservative party had not declared any spending relating to travel in the accounts it submitted for the Hartlepool byelection – even though the prime minister flew to the north-east for a visit that involved electioneering. The Tories and Downing Street both insist that the proper rules were followed, and that it was appropriate for the government to cover the key costs of Johnson’s travel to the constituency. However, Angela Rayner, Labour’s deputy leader, said Johnson had “clearly broken the ministerial code”, which says: “Where a visit is a mix of political and official engagements, it is important that the department and the party each meet a proper proportion of the actual cost.” She has written to the independent adviser on ministerial standards, Christopher Geidt, to demand an inquiry. “Yet again the prime minister behaves like the rules don’t apply to him,” she said. According to the Insider website, Johnson’s first byelection visit to Hartlepool was on 1 April when he flew by private jet from Stansted airport to Teesside, where he made a visit relating to the minimum wage before campaigning in the byelection. He subsequently made two more campaign visits to Hartlepool. It is not unusual for ministers to combine government business with party political business when they are on visits outside London, but when this happens, the party is supposed to contribute a share of the costs. However, Insider found that the Tory spending return for the byelection put the transport costs associated with the campaign at “nil”. Downing Street said the prime minister visited Teesside on official government business, and that “this was followed by a short political visit, as permitted by the ministerial code”. No 10 said all costs had been “appropriately proportioned” and that there was no need for the Conservative party to cover the costs of Johnson’s travel by car because the ministerial code says ministers needing higher security can use government cars for party purposes. The Conservative party said it had covered “all relevant costs” associated with the prime minister’s visit on 1 April, but a party source implied this did not include a contribution to the cost of the flight, saying the flight was “for a government visit and was government staffed, and not in the Hartlepool constituency”. No 10 has also refused to confirm that the Tories contributed to the cost of the flight.