Defendants in a multi-million pound civil claim are appealing a high court judgment.

The case focuses on the redevelopment of the grade 1-listed Cornwall Terrace on the edge of London’s Regent's Park.

Developers the island-based Oakmayne Group were behind a scheme to convert the building to prime residential properties to sell to high-net-worth individuals.

But the development project was hit by increased building costs and construction delays, leading to its failure with losses of £43m.

Claimants Matthew Wickers, Dennis Lavin and John Tinsley were persuaded to invest sums totalling £1.2m, £1.25m and £1m respectively.

Each of them lost their money when the project failed.

Judgment handed down last June following a six-week trial in 2024 concluded they had been duped into investing in the project.

Deemster Alan Gough found that the investment opportunity brochure was a ‘fraudulent document’ which mis-stated facts and deliberately omitted or disguised matters, not least the £3.7m ‘success fee’.

Island-based defendants, David Humbles, Michael Riddell and Guy Wiltcher all directors of Oakmayne Properties (Regeneration) Ltd, now in liquidation, were subsequently ordered to pay costs.

But they have now lodged an appeal.

The case will be heard in the appeal court over five days between March 23 and 27.

Cornwall Terrace was constructed between 1821 and 1823 to a design by Decimus Burton, and under the supervision of John Nash, who designed Buckingham Palace.

For the six-week hearing in 2024, there were more than 8,500 pages of documents in the trial bundle, six experts’ reports and more than 350 pages of written submissions.

Oakmayne had secured some £170m of financing from the banks for the project - with a condition that a further £40m had to be sourced from private investors.

Increased building costs and construction delays led to the project failing by 2013 at the latest, with losses of £43m. All the properties were eventually sold but at prices that did not bring any return to the private investors.

The banks exited largely unscathed, but the claimants each lost their original £1m investment plus extra money they had injected into the venture.

Mr Wickers, Lavin and Tinsley maintained matters were concealed from them so that they did not appreciate the true picture regarding the failure of the project until 2014 or later.

They also queried the payment by directors of the ‘success fee’ of £3,763,735 to Oakmayne Properties (Regeneration) Ltd.

In September last year, Deemster Gough ordered an interim payment on account to the claimants of costs in the sum of £1.1m plus VAT to be paid within 28 days.

The claimants had estimated their costs at £2.5m but the Deemster reduced this to £2.25m taking into account that while their claim which was predominantly successful, part of it was not.

The Deemster ordered that interest on the judgment sums be paid at 4% per annum from the date of each loss to June 2019 and at 8% per annum from that date to the date of judgment.