Police in Theresa May’s constituency have stopped questioning suspected shoplifters in a drastic cost-cutting move.

Thames Valley Police believe the unprecedented step will save thousands of pounds a month and free up officers to respond to emergencies.

Under the ‘no interview’ policy, if detectives think they have CCTV of someone shoplifting, they can simply charge them without quizzing them first.

But experts warn that the force risks breaking strict laws on police procedure and even the right to a fair trial, because officers are meant to investigate all lines of inquiry – including any alibi or defence a suspect may have.

If detectives believe they have CCTV of somebody stealing, they will charge them without interviewing first

Barrister Simon McKay, an expert on policing law, told The Mail on Sunday: ‘The interview is an opportunity for the police to identify reasonable lines of inquiry, including those that may point away from the suspect – a critical aspect of the investigation of crime and a valuable safeguard for those accused of crime. In the wake of a series of near-misses, a policy of this nature undermines the spirit of the disclosure regime and is an affront to principles of a fair trial enshrined in English and European human rights law.’

Thames Valley Police – which covers the Prime Minister’s Maidenhead constituency – have had to make £99 million of savings since 2010 and must make another £14 million of cuts by the end of the decade.

The force, covering Oxfordshire, Berkshire and Buckinghamshire, is facing ‘stark choices’ such as axing its mounted section and is hiring up to 100 civilian ‘case investigators’ because it is so short of officers.

Internal documents seen by The Mail on Sunday show the force carried out a pilot project at its Abingdon custody suite in which 35 suspects were ‘charged without interview’ – saving ‘105 hours and £2,310’. The report said: ‘As demonstrated by the early guilty plea rate, not interviewing eligible suspects does not have a detrimental effect on successful prosecutions.’

The areas affected by the 'no interview' policy of Thames Valley police include prime minister Theresa May's constituency

Another report added: ‘The Abingdon custody “no interview” trial has now been rolled out across the force with the successes of the original scheme being reproduced, in time savings and positive outcomes.’

A spokesman for the force insisted the ‘no interview’ process was legal, was being used only for suspected shoplifters and only in certain circumstances.

‘In order to enable officers to move straight to charge a suspect rather than arrest and interview, there is a very clear set of criteria that need to be met,’ the spokesman said.

‘The key one being overwhelming evidence – for example, CCTV evidence of sufficient detail and quality.

‘If all of the criteria are met, the officer can charge and produce a file for court. This approach is being adopted by our other custody suites but is limited to shoplifting offences.’