A Ukip MEP has defected to the Conservatives as his former party claims he had been suspended after an investigation into “extremely serious” financial issues, evidence of which it says has been passed to the police.

Amjad Bashir, communities spokesman and MEP for Yorkshire and the Humber, dismissed Ukip’s claims as “absurd and made-up allegations”.

Bashir told the Sunday Telegraph Ukip had become a “party of ruthless self-interest”, was “pretty amateur” and had a “ridiculous” lack of policies.

He said: “After almost three years as a party member, I realise that Ukip is more concerned with furthering its own interests as a political party than delivering for the British people. I’ve seen Ukip both at home and abroad, and I’m sorry to say they’re pretty amateur. In the European parliament, some of their MEPs think it’s acceptable to shout and fool around.

“They think they’ll sweep up dozens of seats in May, but that’s delusional. What they are in very real danger of doing, however, is making a big enough dent in the Conservative vote to let Labour in.”

David Cameron told the Sunday Telegraph that he was “absolutely delighted” by Bashir’s decision.

Cameron said: “I’m absolutely delighted that Amjad has decided to leave Ukip and join the Conservative Party.”

Bashir, who is a Muslim from a Pakistani background, had an “inspiring” story, the prime minister said. “It’s another sign that in this great country of ours you can come to Britain without very much and you can be a member of the European parliament, an MP, sit in the cabinet.”

He said that he understood why some Conservative supporters had drifted away to Ukip. “I want to genuinely win those people back by saying, ‘Look, we are the only party that can offer the strong immigration control this country needs; we are the only party that can deliver that referendum that the British people deserve.’ ”

News of the defection emerged shortly after Ukip issued a statement saying it had suspended Bashir and would be passing information from its investigation to the police. The party’s leader, Nigel Farage, described the allegations, which include claims of interference with the candidate selection process, as “extremely serious”.

A party source said Bashir had been aware for some time that he was being investigated and suggested that the suspension was the reason for his defection. “He knew he would be receiving that letter today,” the source said.

Bashir had been informed he was facing investigations that include unanswered financial and employment questions, interference with Ukip candidate selection processes and a continued affiliation with Mujeeb Bhutto, a former Ukip spokesman who resigned from the party after it emerged he had been jailed for his part in a Pakistani kidnapping gang.