A former Metropolitan police detective who successfully sued the force for wrongly using its powers to investigate her has lost her eight-year court battle to hold the police to account.

Andrea Brown said after a new ruling against her she might become homeless paying the police’s costs. “It can’t be right that the police have been found to have acted unlawfully but I’m the one being punished,” she said.

Brown, 53, had 20 years’ service in the Met and was considered by her bosses to be an example of the force’s commitment to diversity. For many years a portrait of her policing a football match hung in the foyer of Scotland Yard.

Her problems began in 2011. Her father died while she was on sick leave and she travelled to Barbados to visit relatives with her mother and 14-year-old daughter.

She informed her Police Federation representative that she was making the journey but not her immediate boss at Sutton police station. This was a minor disciplinary offence. However, instead of treating it as such, her boss approached the National Border Targeting Centre, which Greater Manchester police (GMP) help to run, to get personal information about Brown.

The centre collects private information on people’s whereabouts. An application to trace her movements with Virgin Atlantic was made citing a made-up act of parliament, Central London county court was told.

When Brown discovered what her bosses had done she successfully sued the Met and GMP. She succeeded on claims for breach of data protection and human rights and misuse of private information but lost on a claim for misfeasance in public office and on a personal injury claim.

The two police forces offered to settle the case out of court for a total of £18,000. Brown rejected the offer, saying she was fighting the case on a point of principle. She said she wanted to ensure that other officers did not go through what she had gone through, and she wanted officers found by the court to have acted unlawfully to be disciplined.

The court ruled she should be awarded £9,000 in damages. Because this award was lower than the offer made by the police, she became liable to pay police costs from the point in time the offer had been made. The costs rules were found not to protect her from that liability because her case included non-personal injury claims.

She has had to sell two successive homes to pay legal fees to continue fighting the case.

This month the case reached the court of appeal. The judges there were asked to rule on whether people with cases like Brown’s should have to pay the other side’s costs if they won certain damages cases but rejected offers to settle out of court and were then awarded lower damages.

The court ruled against her and she is now liable to pay the legal costs for the Met and GMP. The bill has not yet been finalised but could run into tens of thousands of pounds.

“I had to downsize and move out of London to Suffolk because of the costs of this case,” Brown said. “Now that the court of appeal has ruled against me, I might have to sell my current home and may end up homeless. My mum told me she has got some money saved up for her funeral that she will give me to help me pay the costs, but I can’t take that money from her.”

Brown hopes a crowdfunding campaign will help. She said she was devastated by the appeal court ruling. “My fight has been a fight for everyone who feels they have a case against a big organisation.

“I brought this case because the police should be held to the high standards they expect from others. Nobody should be above the law. I don’t like injustice, I never have, that’s why I joined the police in the first place.”

In their ruling, the three appeal court judges said: “The proceedings following the appellant’s rejection of the offer were a waste of time and money for all parties, having been necessitated only by the appellant’s refusal to accept much more than she eventually recovered.”

A spokesperson for the Metropolitan police service said: “The MPS has successfully defended a civil claim for malfeasance in a public office brought by former officer Andrea Brown at the high court. The MPS admitted liability for claims concerning breaches of the Data Protection Act and Human Rights Act.

“A judgment in favour of the claimant was formally entered in respect of the accepted parts of the claim. The court also found in the applicant’s favour for a claim of misuse of private information. “A final judgment and ruling on damages is awaited from the court and expected in the near future, and therefore at this stage we will not be commenting further on the case.”

GMP have been approached for comment.