Parliament’s security chief has abruptly quit after a series of debacles, it can be revealed.

Alison Giles suddenly resigned as Director of Parliamentary Security last month and has been replaced by a predecessor once accused of being too close to MI5.

She was praised for her five years of service in a notice on the staff intranet – but senior figures believe she was made the ‘fall guy’ for a series of high-profile failings in the past year.

Ms Giles was blamed by some for £10million of taxpayers’ money being spent on a new front door to the House of Lords that did not work properly.

She has also faced anger from MPs and peers over the building of a ‘hideous’ fence along the boundary of the Palace of Westminster.

And her department faced further embarrassment when, as the Daily Mail first reported, an intruder broke into Parliament in broad daylight and got into the heart of the estate before being spotted by a workman.

In a reference to the fiasco of the Peers’ Entrance, one source said: ‘There are many people in the Lords who believe she was made the fall guy.

‘It was the view of a fair number of people that the chief executive should accept responsibility for what was at the time the biggest project.’

The plan to improve safety was devised in the wake of the 2017 Westminster terror attack, but cost far more than planned and was delayed by two years.

The full £9.6million cost was made public only last June as peers declared it was ‘completely unacceptable’ that the door still did not work properly.

As recently as last month, the revolving door had mechanical faults and it now has to be checked at 8am every day ‘to monitor for any issues’, internal papers admit.

A Parliamentary written answer confirmed last year that the Director of Security for Parliament was ‘the Executive Sponsor for the Security Construction Programme’ and ‘accountable for setting the requirements and assuring the achievement of the benefits for Parliament’.

Ms Giles’s salary and benefits stood at between £150,000 and £155,000 in 2024-2025.

Her departure has not been publicly announced but a statement published on Parliament’s intranet last month stated: ‘Director of Parliamentary Security, Alison Giles, is leaving Parliament after five years leading our bicameral security team – the Parliamentary Security Department.’

Marianne Cwynarski, Director General in the House of Commons, said: ‘I want to thank Alison for the contribution she has made in her five years in Parliament.’

Her interim replacement Paul Martin once led an arm of MI5 then known as the Centre for Protection of National Infrastructure (CPNI).

He took up Ms Giles’s role last month, having last held it between 2013 and 2016 when he was at the centre of a row over his close links to the security services.

Serjeant at Arms Lawrence Ward quit his job over the ‘apparently untrammelled power being given to Mr Martin’ and said Parliament had to decide if it wanted to hand security to someone who ‘remains a pass-holding member of the security services’.

A Parliamentary spokesman said: ‘Alison Giles has decided to resign following five yearsleading Parliament’s bicameral security team.

‘Paul Martin has been appointed as interim Director of Parliamentary Security, bringing more than three decades of national security experience to leading day-to-day operations within Parliament.’