May was accused of a lack of “humanity” after she dodged survivors of the Grenfell Tower blaze during a swift 15-minute tour of the site in the immediate aftermath.
But at the Savoy event – where tables cost up to £5,000 – the Prime Minister posed for selfies and a bottle of champagne was raffled to raise funds.
Ian Lavery, chairman of the Labour Party, hit out at May’s decision to attend the event, adding: “At a time when the country is facing some of the most difficult and challenging times in recent memory, it speaks volumes of the Prime Minister that her priority was to spend time raising money for the Tories.
“One day before the Queen’s Speech and in the midst of the Brexit negotiations, Theresa May should be focused on providing the leadership this country so badly needs, not wining and dining big Tory donors so that she can refill her party’s election coffers.
“This is yet another example of the appalling lack of judgement and tact she has shown over recent days. The British people deserve a government that will stand up for the many; what they’ve got is a Prime Minister and government that always stands up for the few.”
A Conservative source told HuffPost UK: “The Prime Minister was honouring a long-standing commitment.”
Asked if she had considered resigning over Grenfell Tower on Monday, the PM’s spokeswoman said: “The Prime Minister is chairing Cobra right now, later on today she’ll meet the Irish Taoiseach, after that she will chair a third meeting of the Grenfell Tower taskforce, on Wednesday her government will set out a Queen’s Speech, on Thursday she goes to the European Council.
“These are incredibly challenging times, with two terrible incidents in recent weeks and she’s leading the country through them.”
At the Savoy event, which HuffPost UK attended, May devoted almost an hour of her time to party members, delivering a lengthy speech and joking the election result “didn’t turn out quite as I planned”.
Guests ate a green asparagus salad with truffle and soft boiled egg, followed by slow roasted salt marsh rump of lamb with caramelised heirloom carrots and a tarragon jus.
Among the guests at the luncheon were a string of wealthy City bankers and Ukrainian-born British businessman Alexander Temerko, who has provided a steady stream of cash to the Tories when David Cameron was leader.
The event, was organised by the Cities of London and Westminster Conservative Association – which is among the wealthiest Tory groups in the country.
The Prime Minister told them: “I have heard tales of this lunch in the past and now I have actually experienced what a wonderful event it is, so (…) congratulations to you and all those who put this lunch together and who gather this amazing crowd of people and who support the party and support your effort in cities of London and Westminster which is a unique constituency if you think about it.
“It is home to our monarch, it is home to our parliament, the home to one of the great financial centres of the world.”
The Prime Minister said the recent terror attacks and the Grenfell Tower fire had shook London as she stressed the importance of uniting as a city.
“Sadly as we meet here today, we do so against the backdrop of tragic events which have taken place in London in recent months,” she said.
“Three terrorist attacks, the most recent in the early hours of Monday in Finsbury Park and of course the absolutely horrific fire at Grenfell Tower.”
She said: “This is one of the greatest cities in the world and long may it continue.”
But she then went on to talk about the Tories’ disastrous election, in which the party lost its majority.
She said: “But of course we meet today, we also meet against the background of a general election, which … didn’t turn out quite as I planned it.
“I called it. I don’t have a majority, so I accept my responsibility. What we have to do now is recognise there were some good things, we [had] over 42% of the vote, our biggest vote share for 30 years.
“In many elections in recent decades, that might actually have been a landslide victory, but it wasn’t.
“We did win seats that we have never held before in other parts of the UK. We won Mansfield, Walsall North, North East Derbyshire – these are places we have never seen a Conservative MP.
“But sadly the results here in London were not so good for us. We have look at what we did right in the campaign and what we did wrong.
“One place where we did see success was in Scotland and while we may not have got the overall majority in Westminster that we might have wanted but I think as a result of what has happened, we might have saved the United Kingdom.”
She referenced the Queen’s Speech, which will be put before Parliament tomorrow setting out her programme for government over the next two years.
But her words came as it emerged the deal she expected to strike with Northern Ireland’s DUP was stalling.
She said: “We need to make sure we get on with the job of governing so the Queen’s Speech in Parliament will take place tomorrow.
“We do this against a backdrop of huge challenges – the Brexit negotiations which started yesterday and we have got to get that right.”
Her speech to party members also came as car manufacturers with the Society of Motor Manufacturers and Traders (SMMT) met just yards away, amid fears the country could slide off a “Brexit cliff edge”.
“Let’s go out there and show what we as Brits are made of, and the success that we can make of our economy,” she said.
“I won’t pretend that this is the easiest job in the world to do.
“I won’t pretend that there aren’t uncertainties and that there won’t be, y’know, barriers in the way that we have to overcome but I believe that when we come together, as one United Kingdom, and recognise our strengths, our abilities and our talents, we make the most of those.”
Conservative association chairman Patrick Evershed pleaded with the super-rich guests to hand over cash before he introduced the prime minister.
He asked those gathered to show “even more generosity” because “times are very tough”.
He said: “This election is not what we all hoped for and it certainly is not what we deserve. Despite that Theresa May got 5% more votes than David Cameron did two years ago.”
“We need a lot more to do even better than we have in the last one, so please be very generous.
“The minimum prescription is 25 but I think several of you here are pretty well off.”
The party received £12.7m in donations between May 3 and June 8, while Jeremy Corbyn’s Labour Party received £4.5m and the Lib Dems £1.1m.
The Government has also stressed the Prime Minister is making “some progress” in helping Grenfell Tower victims after a fund was set up.