2 hours ago

Nick Eardley, Political correspondent and

Paul Seddon, Political reporter

PA Media

Mandelson was pictured outside his London home on Friday

The prime minister will appear before MPs on Monday to explain what went wrong, after it emerged that Lord Mandelson did not pass inital security vetting checks ahead of taking up the role of ambassador to the United States.

But there are some key questions that remain unanswered.

Did the prime minister and the government mislead MPs - and the public?

The prime minster has said he only found out this week that Lord Mandelson had failed developed vetting (DV) – an intrusive process designed to ensure that people with access to secret information, like ambassadors, do not pose a potential security risk.

A day before Lord Mandelson was sacked last September, the prime minister told MPs that "full due process" had been followed during his appointment.

But the day after the peer was dismissed, The Independent raised questions about that process,…