The Conservatives' poll ratings hit an unprecedented low today, dashing hopes that the sentiments around the death of Margaret Thatcher would help boost David Cameron's popularity.

The latest YouGov survey puts the Tories at 28%, compared to 42% for Labour and 12% for the Liberal Democrats. Ukip is on 11%.

YouGov is the third polling company to report the Tories at their lowest ebb, after Opinium and TNS BMRB.

David Cameron's popularity rating is unchanged at 31% but Ed Miliband's actually climbed by two points to 22%.

The findings come as further details were released about Thatcher's funeral, including who will be invited.

Argentinean president Cristina Fernández de Kirchner has been snubbed amid continued tensions over the Falklands but controversial figure FW de Klerk, the last president of apartheid in South Africa, will be attending.

Invitees include:

All surviving former prime ministers

All surviving former US presidents and a Reagan family representative

Hillary Clinton

All surviving members of Lady Thatcher’s Cabinets

The current Cabinet

The leader of Her Majesty’s opposition

President Manuel Barroso

Sir Bernard and Lady Ingham

Fredrick Forsyth CBE

Former prime minister Mahathir of Malaysia

A representative of Nelson Mandela

Mr & Mrs Michael Portillo

Tony & Cherie Blair

F.W. de Klerk

Dame Shirley Bassey DBE

Jeremy Clarkson

Lord and Lady Lloyd Webber

Lord and Lady Archer

Lord Powell of Bayswater KCMG OBE

Lord Carrington

Prime minister Harper of Canada

Former prime minister Brian Mulrooney of Canada

The Queen's attendance continues to create controversy, with many saying it elevates the occasion to a state funeral in all but name – an honour not given to other major British prime ministers like Clement Atlee.

That controversy could just be the tip of the iceberg, as more evidence emerges of disagreement about how to handle the death behind the scenes in Westminster.

It is understood Speaker John Bercow objected to the decision to recall parliament yesterday for the unprecedented seven-hour debate on the former prime minister.

The Speaker is reported to have argued that MPs could have debated her legacy on Monday, when the Commons was set to return from the Easter break.

The costs of yesterday's recall were significant. When parliament returned due to the summer riots in 2011 it cost the taxpayer £43,857 – not including the travel expenses of MPs travelling back to London from anywhere in the world.

But it is understood David Cameron enlisted the support of Ed Miliband to win over Bercow. He also plans to cancel prime minister's questions next Wednesday – the day of the funeral - and allow the Commons to sit later.

Meanwhile, it emerged the Foreign Office told diplomatic staff in embassies around the world to wear black for mourning on the day, although that advice was later retracted. Officials put it down to an administrative error.