Ukip is facing financial ruin following a slump in membership and the loss of key donors in the wake of the party’s disappointing General Election performance, The Mail on Sunday has learned.

Insiders say the situation has become so desperate that many staff wages went unpaid last month, and leader Nigel Farage has been forced to ring round backers begging for a financial lifeline.

The problems have been compounded by the fact that the party’s biggest donor, Arron Banks, is now channelling his money instead into his own campaign for the UK to vote to leave the EU.

Insiders say the situation has become so desperate that many staff wages went unpaid last month, and leader Nigel Farage has been forced to ring round backers begging for a financial lifeline

It is understood that since the Election – when Ukip managed to win just one seat – the party membership has lost around one quarter of its 50,000 members, wiping £300,000 from annual revenues.

It comes as the party hopes to mount a strong challenge in the Oldham West and Royton by-election next month, which is being fought after the death of Labour’s Michael Meacher.

One party source blames ‘Nigel’s U-turn’ – when Mr Farage resigned as leader in the wake of his failure to win the Thanet South constituency only for him to change his mind shortly afterwards – for alienating supporters.

Ukip’s only seat came from Douglas Carswell, defending the Clacton constituency he won in a spectacular by-election victory.

Ukip received a total of £3 million from donors in the first four months of this year, but in the three months since the Election, the money coming in from donors and public funds is believed to have been less than £200,000.

The problems have been compounded by the fact that the party’s biggest donor, Arron Banks (pictured left), is now channelling his money instead into his own campaign for the UK to vote to leave the EU

Ukip’s only seat came from Douglas Carswell (right), defending the Clacton constituency he won in a spectacular by-election victory.

The crisis has led to nearly half of the party’s workers at their Devon head office being made redundant, and wages and bills going unpaid.

A senior party figure, who played an influential role in the Election campaign, said that Mr Farage had also been horrified to be hit by unexpected bills – such as an invoice for nearly £80,000 from Facebook for the costs of social media campaigns, plus business rates and other costs relating to a Mayfair office.

Last month, some staff failed to receive their pay cheques at all, and were only given partial salaries after bridging finance was found. The figure said: ‘It is a total car crash, unpaid bills everywhere including the poor people who paid for coaches and transport to take people to Mr Farage’s personal campaign.’

Mr Banks became Ukip’s biggest donor last year when he handed Mr Farage £1 million. He now runs Leave.EU, one of two ‘Out’ campaigns in the EU referendum, which claims to have more than 200,000 supporters and millions of pounds in pledged backing.

A Ukip spokesman said: ‘It was predicted that we could not pay our bills for the General Election in July, and that was not correct. The suggestion that we had a problem meeting payroll last month is also incorrect. It is certainly true that having a competitor like Leave.EU presents a challenge. As we are no longer the only game in town, we have to try harder to attract supporters, but our members know that without Ukip there would have been no referendum for Leave.EU to campaign in.’