Volunteers could be deployed to help plug gaps in the UK’s Border Force, which has undergone drastic cuts under successive Conservative-led governments.

The plan, similar to the use of special constables in the police, is being considered in Whitehall. Critics, however, say doing so would be risky and caution against using a “Dad’s Army” to guard Britain’s frontiers.

Under the proposal, teams of volunteers would be used to bolster staffing levels at the Border Force, which manages immigration and customs controls. The government stressed that involving volunteers in immigration enforcement was not under discussion.

Concerns have been raised in recent years about the coverage of dozens of minor harbours and landing places in the UK. “Small ports and airfields are a known security weakness in our border security, so it’s important to ensure that security is stepped up, particularly to stop illegal immigrants and returning Isis fighters,” said Charlie Elphicke, the MP for Dover.

But he told the Mail on Sunday: “Border security is a skilled job, which takes many years of training. I would urge great caution before seeking to adopt a model like that used by the police, with special constables. We can’t have a Dad’s Army-type of set-up.”

Yvette Cooper, the Labour MP who chairs the parliamentary home affairs select committee, told the paper: “Filling the gaps with volunteers because of budget and staffing cuts raises very serious questions about border security and the Home Office commitment to this important public service.”

Mark Serwotka, the general secretary of the PCS union, which represents many of the Border Force’s 8,000 staff, expressed concern about the plan and accused the government of “making our borders weaker with the use of casual labour”. He said it was “risking this country’s security on the cheap”.

“In the last year, the Home Office have increased the use of agency staff, spending a staggering £25m last year to agency firms, a £5m increase on the previous year,” he said.

“Border Force are already using poorly trained seasonal workers at most ports and airports, not just at peak periods but throughout the year because of permanent staff cuts. The plans to use volunteer Border Force specials is a further move towards casualisation of the workforce.

“Government rhetoric has claimed that they are ‘strong and stable’. That is not the effect of their policies on this country.”

An inspection published earlier this year of 62 ports, wharves, marinas and jetties on the east coast that were normally unmanned found Border Force officers had not been to 27 of the sites during the 15 months from April 2015 to June 2016.

The assessment said one of the risks of long periods of non-attendance was that there was “no visible deterrent to anyone prepared to risk using these spots to land illegal migrants or contraband”.

In a separate report, the former independent reviewer of terrorism legislation David Anderson QC also flagged up coverage of smaller south and east coast ports, marinas and landing places, saying it was conceivable they might be an option for returning foreign fighters or other terrorists.

The Home Office said the Border Force had a good record and that the government was committed to ensuring that it had the necessary resources. “We will never compromise the security of our borders,” a spokesman said.