Thunderstorms are threatening to bring more unwanted rainfall to a Derbyshire town where a damaged dam is thought to be at risk of collapse.

Dozens more homes have been evacuated in Whaley Bridge before bad weather expected from Sunday afternoon, as emergency workers continue their efforts to prevent the dam giving way.

Fifty-five homes in the Horwich End area of Whaley Bridge were cleared on Saturday evening, two days after 1,500 residents left town.

Water levels at the Toddbrook reservoir in Whaley Bridge have been reduced by 1.3 metres since Thursday, but the condition of the structure remains “critical”.

Police said the additional evacuations were undertaken because of “a potential increase in risk of adverse weather in coming days and the ongoing risk of the Toddbrook reservoir breaching”.

Whaley Bridge: storms forecast as work to repair dam continues Read more

Derbyshire police allowed one person from each of the 400 Whaley Bridge properties evacuated on Thursday to return for a 15-minute visit on Saturday to pick up pets and other essentials.

At the Horwich End traffic lights on the Buxton side of the town, cars queued to get through the police blockade. Officers have stopped people entering the steep-sided village since Thursday afternoon when a month-and-a-half’s rain fell on the Derbyshire hills in just 48 hours, causing damage to the 180-year-old dam at Toddbrook reservoir.

Engineers deemed there was a “substantial risk to life” should the reservoir fail, prompting the evacuation of the lower quarter of the town.

Ania Hill had been worrying about her cat, Slippers, ever since the evacuation. She was relieved to find him alive but distressed. He had not gone hungry after a neighbour managed to throw him food through the letterbox. “He was quite upset, I’ve had to put him in the dark in the boot to calm him down,” she said after her personal rescue mission.

Play Video 1:31 RAF helicopter joins effort to stop Derbyshire dam collapse – video

Police had stipulated that only one person per household would be allowed through the cordon. Visits were to be timed, with residents signing in and out. But in practice, many people had brought a friend or spouse and took longer than their allotted 15 minutes, as an RAF Chinook helicopter ferried bags of aggregate to drop on the damaged dam.

Gail and Martin Shaw, who live on Buxton Road, the main road through the town, took the opportunity to return home and move more belongings – furniture and Gail’s collection of ornaments – upstairs.

Like many residents, they take seriously the warning from engineers who said on Friday night that they remained very concerned about the integrity of the structure, despite an extensive pumping operation having reduced water levels in Toddbrook reservoir.

They were also worried about looters after Martin returned on Friday night to see two men trying to break into his shed. “It was two fellas, their trousers all wet – I think they must have entered the village via the River Goyt, which runs right behind our house,” said Martin.

Derbyshire police said it would look into the claims of looting, with a press officer saying she was unaware of problems of that nature following the mass evacuation.

Fred Salmon, who runs the Bike Factory shop in the centre of the town, arrived with his van, hoping to bundle as many bicycles in the back as he could. Another woman, rushing too much to give her name, speed-walked to her house to pick up her passport: she was off on holiday later in the day.

Dan Curley, the landlord of the Cock pub on Buxton Road, was finally allowed back to fetch his spectacles, having spent the first 36 hours after the evacuation with a splitting headache.

Peter Drinkwater was among those allowed to return to his terraced cottage. “Until the evacuation, I’d never spent a night away from the house in 37 years,” he said after retrieving a selection of clothes and medication.

His daughter, Cathryn Swann, said: “It feels really eerie down there. The police had told us to come straight back if we heard any rumbling sounds, and of course there was rumbling anyway from all the aggregate being dropped on to the dam. I panicked a couple of times, but thankfully we’re OK.”

Ruth George, the local Labour MP, who lives just outside Whaley Bridge, arrived to find out the latest news.

Facebook Twitter Pinterest A Chinook helicopter prepares to drop sandbags onto the dam wall at Toddbrook reservoir. Photograph: Leon Neal/Getty Images

She said she had written to Boris Johnson on Friday night after his visit. He told residents that he had flown over the dam and thought it was “dodgy but stable” and assured them they would all be rehoused should the worst happen.

In her letter to the prime minister, George asked him to ensure a proper investigation into why the reservoir dam had been damaged and to ensure it could not happen again. “It’s not just about the emergency situation, as important as that is,” she wrote. “Whaley Bridge as a town needs to be able to feel safe for the long term and we need to know what the options are.”

She commended the emergency services but warned that the situation remained critical. “We’re expecting lots and lots of rain over the next few days so I can quite understand the authorities not being prepared to say it’s safe until those storms have gone.”

Edwina Currie, a former Conservative MP who lives in one of the higher parts of the town, said: “Our reservoir is looking like it’s in intensive care at the moment. There are pipes everywhere giving it the treatment it needs. But we are a sturdy lot up here and you won’t hear us complaining.”

The environment minister Thérèse Coffey said the situation remained in a “critical stage” on Saturday as she issued a message to residents.

“I cannot emphasise enough how patient they need to be,” Coffey told BBC Radio 4’s Today programme. “Of course this is a distressing and worrying time for them, but if that dam were to breach it would lead to a loss of life if there were people there. There’s no doubt about that.”