Pioneering “Hobbit house” couple Heidi and Sav Pavlou are not in their new home for the start of 2017.

Mum-of-five Heidi said: “We were hoping to be in by now but, as always on projects like this, things have gone slower than expected. It’s a little disappointing, but it is still going to be worth it in the long run.”

The couple sold their home in Newington at the start of the year and began work on what is believed to be Britain’s first below-the-surface “ground house” on May 16 at Brambledown, where Heidi grew up.

Much of her family spent Christmas at her parents’ house in Minster. The extraordinary project was originally going to cost the couple £180,000.

But Heidi admits it is now, in the best tradition of the TV show Grand Designs where she first saw the concept, over budget and could cost up to £280,000.

Video: The 'Hobbit House' takes shape

The eco-house walls are made from 800 recycled car tyres filled with chalk, covered in London clay and clad in Kentish ragstone and flint.

The giant double-glazed south-facing full-length windows were installed just before the weather changed, and this month the intrepid couple and their crew – including a team of prisoners – finally sealed the roof with rolls of rubber ready for it to be covered with earth.

But the inside remains a building site, still with no floor.

Heidi said: “We are very proud of how far we have come and would like to thank everyone who has helped, including local companies like Steve Mutton of Fences R Us and Mike Rudd of Grandview Gardens. There is still loads to do, but we are having a break over Christmas.

“We only had to stop for two days and that was to get building work signed off. The building inspectors have been on the ball the whole time. They scrutinise everything because it is new to them as well.”

So when will it be ready? Heidi has set a new date for May 16. She said: “We started on May 16 so we should be in within a year. It’s just that it would have been nice to have been in for Christmas.”

Highlights so far

August: First wood posts of front windows installed on dwarf brick wall

September: Post Office officially recognises address as Groundhouse Sheppey

October: Surprise visit from Nick Knowles and the team of the BBC TV show DIY SOS, who were working on a project at the end of the road

November: Inside temperature of house registers 17C despite being -2C outside and the roof still not being sealed

December: Roof finally sealed using Firestone products by LSF Building Services