LONDON (AFP) - A British woman and her husband were found guilty on Friday of murdering her parents and burying them in their own back garden, where they lay undiscovered for 15 years.

Susan and Christopher Edwards killed the elderly William and Patricia Wycherley, aged 85 and 63 respectively, in 1998 but kept up the pretence that they were still alive.

Susan Edwards sent Christmas cards and letters to relatives telling them her parents were travelling in Ireland "because of the good air", and told neighbours they had moved or gone away.

In the meantime, she and her husband, now aged 56 and 57, emptied the couple's bank accounts, collected state handouts on their behalf and even sold their home with the bodies buried in the garden.

The Edwards, from Essex in southeast England, made a total of £245,000 (S$520,000) out of the victims, much of which they spent on film star memorabilia.

But they struggled with debts, a fact that ultimately led to their undoing last year.

Christopher Edwards asked his stepmother for money and admitted that he had helped his wife bury her parents at their home in Mansfield, in central England.

The stepmother called the police and the couple surrendered from France, where they had fled, penniless, in 2012. The bodies were found in October last year.

Susan Edwards had denied murder, claiming she had been provoked into killing her mother after hearing her shoot her father at their house.

She said her husband later helped her to bury the bodies, and insisted they only continued to claim the couple's pension and welfare benefits to cover up the shootings.

However, the jury at Nottingham Crown Court unanimously found the Edwards guilty of murder. The judge warned they could face life in jail when they are sentenced on Monday.

Detective Chief Inspector Rob Griffin, who worked on the case, said the couple acted with "cold calculation and meticulousness".

In a statement, Mr William Wycherley's nieces, Hilary Rose and Christine Harford, said their late mother would have been horrified by the murder of her youngest brother.

"It would have been extremely upsetting for her to discover the deception and lies practised by her niece - our cousin - Susan and her husband Christopher against her and others for so long, for their own selfish greed and gain," they said.

They added that their main priority was now to ensure that the Wycherleys were "finally laid to rest with dignity".