Peter and Lynn Burgess say the transformation of the garden at their £5 million London home would have been completed quicker and more cheaply without her help.

The couple accepted advice from friend Basia Lejonvarn after finding a quote from a professional landscape designer too high, the Daily Mail reports.

After her intervention, they hired contractors to carry out the work at a lower price – but it went awry and they had to return to the original designer to complete the job.

In their legal action, the couple claimed that Ms Lejonvarn owed them a duty of care, but she insisted the advice was offered informally and socially, not professionally.

Judges in the Court of Appeal in London have now ruled that the couple must pay legal costs in the failed case on the indemnity basis, which could total more than £1 million.

Handing down judgment, Lord Justice Coulson said: “There was a time, 30 or 40 years ago, when construction litigation was a byword for expense and delay, and where costs were often out of all proportion to the sums at stake.

“Occasionally circumstances conspire to create a construction case with echoes of the bad old days. Unfortunately this is one such case.”