The Times found debt agents working for British Gas expressed excitement at putting meters in the homes of people who had fallen behind on energy bills.

"This happened when people were acting on behalf of British Gas. There is nothing that can be said to excuse it," Chris O'Shea told the BBC.

The firm has suspended installations.

The move follows an undercover investigation by the Times, whose reporter went with agents working for Arvato Financial Solutions' - a company used by British Gas to pursue debts - to the home of a single father with three children.

After establishing the property was unoccupied, the reporter observed the agents work with a locksmith to force their way in and install a prepayment meter.

It reported that the locksmith said: "This is the exciting bit. I love this bit."

Mr O'Shea told BBC Radio 4's Today programme: "The contractor that we've employed, Arvato, has let us down but I am accountable for this.

"This happened when people were acting on behalf of British Gas. There is nothing that can be said to excuse it."

Agents also fitted a prepayment meter by force at the home of a young mother with an infant baby, the newspaper said.

Others who experienced similar treatment, according to materials seen by The Times, include a mother whose daughter is disabled and a woman described as having mobility problems.

Centrica said the suspension - where it applied to the court for a warrant to install a pre-payment meter - would last "until at least after winter" and that protecting vulnerable people was its priority.

Business Secretary Grant Shapps said he was "horrified" by the findings.

"Switching customers - and particularly those who are vulnerable - to prepayment meters should only ever be a last resort and every other possible alternative should be exhausted," he said.

"These findings suggest British Gas are doing anything but this."

Energy firms are required to have exhausted all other options before installing a prepayment meter, and should not do so for those "in the most vulnerable situations".

It comes amid the rising cost of living and as household bills soar in part due to mounting energy costs.

Why is this allowed and what can you do?

*  Regulator Ofgem rules state that energy suppliers must have effective checks and balances in place when switching the mode of a smart meter

*  The regulator advises customers with concerns to speak to their supplier. Under Ofgem rules they must offer payment plans you can afford and you can ask for emergency credit if you use a prepay meter and can't top up

*  Breathing Space, sometimes called the Debt Respite Scheme, is a free government scheme that could give you up to 60 days' space from creditors to set up a debt solution. Step Change debt charity can help you to apply

*  Citizens Advice offers this guide: Stop your energy supplier moving you to prepayment

Mr Shapps said the energy minister would hold a meeting with British Gas "in the coming days", adding: "He will be demanding answers to ensure this systemic failure is addressed."

A spokesperson for energy regulator Ofgem said: "It is unacceptable for any supplier to impose forced installations on vulnerable customers struggling to pay their bills before all other options have been exhausted and without carrying out thorough checks to ensure it is safe and practicable to do so."

People using prepayment meters pay for their gas and electricity by topping up their meter, either through accounts or by adding credit to a card in a convenience store or Post Office.

This is a more expensive method of paying than by direct debit, but is sometimes the only option for people who have struggled to pay and are in debt to an energy supplier.

Many rented properties also have prepayment meters.

Problems can arise when residents no longer have any credit left on the meter and have no money to top it up - leaving them unable to cook or heat their homes.

Last month, the Citizens Advice charity called for a ban on energy companies "forcing" customers onto prepayment meters because they are struggling to pay bills.

In response to The Times, Gillian Cooper, head of energy policy at Citizens Advice, said: "It's truly shocking to see the extent of bad practices amongst some energy suppliers.

"Our frontline advisers know only too well the desperate situations so many struggling customers have found themselves in. Time and time again we have called for a ban on forced prepayment meter installations until new protections for customers are brought in.

"Ofgem and the government need to act now - serious reforms must be made before these suppliers can be trusted again."

BBC News has contacted Arvato Financial Solutions for comment.