Ukip's spring conference ended in bitter feuding over funding on Saturday night as the party's deputy chairman, Neil Hamilton, accused a top donor of failing to deliver.

Last year Yorkshire multimillionaire Paul Sykes promised to bankroll the party's European elections campaign, handing over "whatever it takes" to ensure that the party topped the poll. At the time the pledge was seen as a coup for Ukip, but Hamilton, a former Tory minister, told the Observer: "So far we haven't seen the colour of his money. This spending needs to be committed. Very large amounts of money can't just start a billboard campaign or publish a newspaper, things have to be planned – there's a lot of creative work involved."

Speaking on the second day of the party's spring conference in Torquay, Hamilton said: "He won't be giving the money directly to Ukip. He has said he will fund certain things: for example, billboards or advertising vans."

In a sign of growing unease about the party's relationship with Sykes, who is thought to be worth around £650m, Hamilton insisted that the businessman, "can't brand anything with Ukip that he might want to do unless I've agreed it. It's our campaign, not Paul Sykes' campaign. Obviously it would have been much easier if the money were in Ukip's bank account and I could plan sensibly for the campaign far enough in advance."

He added that the publicity around Sykes' pledge had been unhelpful – dissuading other members from making donations. He said: "It's been a big problem for us in fundraising and elsewhere, as people say, 'You don't need my money, because Sykes has signed a big cheque'."

Hamilton is also campaign director for the May elections, but his subsequent role leading up to the general election in 2015 is unclear. In a press conference on Friday, Ukip leader Nigel Farage referred to Hamilton as only a "backroom boy" when asked about his involvement in the 1990s cash-for-questions scandal which saw him lose his seat as a Tory MP.

Of his relationship with Farage, Hamilton said: "We have disagreements, but keep those as far as we can private. Not everybody can get everything right ... We have disagreements about how to handle things or what we should be doing." He added that he respected the Ukip leader, saying: "Nigel has been one of the few charismatic politicians in my lifetime who is capable of changing the political landscape."

Pointing out that his role as campaign director will conclude in May, Hamilton indicated that he is unsure whether he will take another senior post in the party.

He said: "Next year's another thing. I'm contracted to do this until May. I don't know what opportunities there will be as yet, but we'll see ... There are things I want to do outside politics."

Party members and Torquay residents packed out the Riviera Conference Centre to hear Farage speak on Saturday. "I would do a deal with the devil," he promised, if it ensured the British public a referendum on Europe.

A new poll published by Opinium/Observer puts Ukip at 19% of the domestic vote, one of its highest poll ratings in the past year.

The party is currently expected to pick up more than a quarter of the vote in the European elections.

The latest polls will provide an added boost to the party after a week in which statistics were released showing a huge increase in net migration. The increase from 154,000 to 212,000 in the year to September undermined David Cameron's pledge to reduce the figure to 100,000 by 2015.

Farage told members attending the party conference that because Britain is unable to challenge freedom of movement within the EU the government is "conning the public that we have a degree of control over this".The two-day conference was also bolstered by German chancellor Angela Merkel's visit to Westminster just a day before, during which she said that while some renegotiation is possible, those expecting her to "pave the way for a fundamental reform of the European architecture" were "in for a disappointment".