Anyone who has followed two decades of war will have found it hard to watch the Taliban seize control of Afghanistan, just days after US and British troops withdrew. But for those who served in the country and are now back in the UK, it has been almost unbearable.

At Catterick Garrison near Richmond in North Yorkshire, the largest British army garrison in the world, the mood among soldiers and ex-soldiers was one of disappointment and despair.

“It’s shameful. The political response has been shameful. I feel completely let down. It feels like we left them to rot,” said Anthony Kirkby, who spent 16 years in the Royal Signals and served in Afghanistan from 2009 to 2010.

“I understand from a moral point of view why we pulled out. But we were not patient enough. We should have been more patient and sat back to give the Afghan forces the edge. We pulled out before they were mature enough to control the situation.”

Kirkby, who was shopping with his partner and child, said Britain had a duty to find homes in the UK for the Afghans he had served alongside. “There’s no doubt in my mind that they will be executed,” he said.

Kirkby, who now works for a software company, also said he had no faith the Taliban would bring peace. “I think within 12 months we’ll see a civil war.”

Drew Elder served 18 years in the Royal Regiment of Scotland, including in Bosnia, Iraq and Afghanistan. He said the men who served alongside the British army in the Afghan national army and the Afghan national police were “decent soldiers and policemen” but they did not have the equipment to do the job.

He said: “I wasn’t surprised to see the Taliban take over. Most people there are either supportive or scared of them.”

The Scot, who now works as a truck driver, feels jaded about the UK’s involvement in Afghanistan. “It’s a pointless episode. It feels like, what was the point? I don’t see why we were there in the first place. We have a lot of cheek to go and fix another country when our own country’s broken; the national debt, politics is a shambles. Everybody lies, it’s just who lies the least.”

Some ex-servicepeople in Catterick Garrison – which, aside from the military vehicles and the buildings surrounded by barbed wire, is an otherwise quiet town centred on a retail park – felt unable to talk about the events they were seeing unfold.

“It’s still too raw,” said one man who served in Afghanistan, shaking his head. “I’ve only been out three years. People aren’t ready to talk about it.”

In a supermarket car park, Adam Black was wearing a Help for Heroes T-shirt. He served as a chef in the British army for 17 years, including two tours of Iraq and a tour of Afghanistan in 2011. He was critical of the west’s handling of the withdrawal.

“It was always going to be problematic. It’s shocking, they just got out as quick as they can. No consideration that boys were lost,” he said. “I feel angry. How long are we going to have to do this? It’s all right bringing people over but how does that help the people there? They’ve just been left to their own devices.

“My son is 17, I was away more than half his life. It’s not good enough. What about the boys who fought there and gave their lives? What about them? It’s a shame what’s happening.”

Kirkby said this was a common feeling among his friends who had returned from serving in Afghanistan. “My overwhelming feeling is of disappointment in the strategy. It’s been really damaging to our standing in the world – what’s left of it.

“I have absolute pride in what we did out there but lots of friends are thinking: what did [soldiers] die for? I’m in WhatsApp groups with friends who served and there’s a huge feeling that it’s been a waste. They think: what was it all for?”