Nigel Farage has admitted breaching parliamentary rules by failing to register a trip to Florida to headline a fundraising event for Donald Trump.

The Reform UK leader was the main speaker at the $500-a-head Republican party dinner in Tallahassee in March.

Guests could pay $25,000 (£18,445) for a VIP ticket, which included having a photograph with the Clacton MP, according to promotional material.

Farage said on Sunday that he had failed to declare the trip in parliamentary transparency logs due to an error by his office. It came after details of the appearance were published by the Sunday Times.

In a statement, the MP said he had emailed details of the trip to his office but said: “Unfortunately, these submissions were not added to the register. This was an error … A correction to the record will be made tomorrow along with an apology to the registrar.”

According to a parliamentary code of conduct, MPs must register any visits outside the UK that cost more than £300 and where the trip is not “wholly” paid for by the MP or by public funds. They must also separately report any “fees” or “payments in kind”. The deadline for doing so is 28 days.

In his statement, Farage said the trip was “remunerated in three separate instalments over the course of two months” but did not say who had paid for it. He added that he had paid for the travel arrangements himself.

Daisy Cooper, the Liberal Democrat deputy leader, said: “Nigel Farage needs to come clean on who’s bankrolling his trips abroad to badmouth Britain. He uses every opportunity he can to talk down Britain and suck up to Trump while failing to represent his constituents in parliament.

“The public deserve to know whether the Trump administration and their cronies are funding these trips, using Farage as a puppet to meddle in British politics.”

Farage missed prime minister’s questions the day before the “Disruptors’ dinner” in Tallahassee, which was organised by the Republican party, on 20 March.

Farage has faced days of scrutiny over the purchase of a house in Clacton, Essex, which initially he said he had bought himself. He later said it was bought by his long-term partner, Laure Ferrari.

This arrangement would have saved the MP an estimated £44,000 in the higher rate of stamp duty to which he would have been liable given that he already owns other properties.

Farage’s lawyers, Grosvenor Law, said last week that they had received written advice from a senior barrister that “concludes that there is no underpayment of SDLT [stamp duty land tax], that SDLT paid was properly calculated and that there is no basis to suggest there has been any improper avoidance or evasion of tax in respect of the purchase”.

Anna Turley MP, the Labour party chair, said: “Nigel Farage has failed to disclose who funded this US trip, refused to answer questions about his tax affairs, and changed his story about where he lives.

“Rather than representing his constituents in the UK parliament to which the people of Clacton elected him, he’s been jetting off abroad to call for sanctions against our country, putting British jobs at risk.”

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