Squatters who moved into Lewisham’s Royal British Legion headquarters for a week left elderly volunteers cleaning up their mess.
The group moved mattresses, computers, games consoles and even a dog into the building in Lewisham High Street from May 29 until June 5.
Members of the charity, which provides support to Armed Forces members, veterans and their families, were "frustrated" when they could not host their fundraising meetings at the venue and lost vital cash.
They spoke to the squatters who argued they were entitled to camp in non-residential property but say they were finally moved on by police after helping themselves to the charity's gas and electricity.
Member of East and Central Lewisham branch of The Royal British Legion, Christine Rosenbaum, said: "We arrived and couldn’t get into the building.
"They had moved in mattresses, computers, game consoles. They did the job thoroughly.
"We weren’t able to do our business. We lost money. This money all goes to charity and keeps us going. It’s a bit frustrating.
"The good news is, they have actually been turned out but there is a bit of damage and it isn’t very clean.
"We are hoping they stay out."
The mother-of-two, whose parents were in the services during the Second World War and helped build the Lewisham building with other British Legion members in the 1950s, fears the charity might be forced to sell the site.
The 67-year-old, who lives in Biggin Hill, said: "Obviously we are going to try to keep it open, but we have got to the point where we will have to consider selling the land. We can’t keep it maintained."
She went on to say many of the members were elderly and the branch was lacking funds.
Branch secretary Doreen Hughes echoed the call for help to keep the site alive and offer a place for ex-servicemen and women to meet as well as raising funds, including for the annual Poppy Appeal.
The 77-year-old said: "The hut itself isn’t in a very good condition.
"There are ex-soldiers that need help.
"There are so many soldiers who can’t talk to civilians about what they have gone through and need somewhere where they can meet.
"Some of the stories are absolutely horrendous.
"They are still going through all this stress."
It comes as police swooped on the boarded-up Catford Bridge Tavern pub and helped to evict 20 squatters.
The group were moved on on May 29 and are believed to be linked to the squatters at The Royal British Legion who arrived later that same day.
A Met spokeswoman said: "We can confirm that police were called to an address in Lewisham High Street on Thursday 5 June.
"Officers spoke with squatters at the scene and asked them to leave.
"The rightful occupier is now back in the premises."
She added there was no damage to the premises and nothing was taken. No arrests were made.
To offer your help or to donate to Lewisham’s Royal British Legion branch email Mrs Hughes at firstname.lastname@example.org
To find out more about the charity visit royalbritishlegion.org.uk