All was going smoothly with plans for the grand opening of a firm's new premises in an old mill until joiner David Hurst revved-up his electric drill.

There was such a squawking and a fluttering from the corner of the room that David had to switch off his drill.

And after rummaging around and finding the source of the commotion he decided work had to stop indefinitely - grand opening or no grand opening.

For there, high on a ledge in a dusty corner of the upstairs room, was a kestrels' nest complete with five eggs.

The noise David had heard was the mother bird expressing her opinion on having her peace disturbed.

And that has posed a problem for Gary Heginbottom, managing director of Artisan Fireplace Design, the biggest retailer of its kind in the UK and the housing development market's biggest supplier and designer.

Now he won't be able to open his new showrooms on time.

"We have moved our head office and warehousing from Bradford Road, Cleckheaton, to bigger premises in Brighouse, increasing the workforce from 20 to 35," he said.

"And our new retail showroom was due to open in early July - with 500 fireplaces on display.

"Now, though, we can't do that. We can't complete the work because the kestrels can't be disturbed until the fledglings can look after themselves. And they haven't even hatched yet."

Kestrels are fully protected under the Wildlife and Countryside Act 1981, which makes it an offence to kill, injure or take an adult, or to take, damage or destroy an active nest or its contents.

"But we wouldn't have carried on with the work if it put the birds at risk anyway," said Gary.

"The nesting pair are beautiful. We'll wait until the eggs have hatched and the youngsters are old enough to fly away peacefully.

"It was a bit of a shock when David found the nest. But he's a bit of an expert and knew immediately he was dealing with kestrels.

"The mother was going ballistic and he said we shouldn't do any more work."

Bird-spotting runs in the family for David, of Southowram. His father was smitten, so was David and so is his daughter.

"As soon as I saw the kestrel I knew what it was," he said. "They are not a threatened species but you don't see that many of them in towns.

"The mill is on a very busy road and there's lots of noise from a building site but it doesn't seem to bother them."

Kestrels eat voles, mice and shrews, small birds, insects and earthworms. In towns they take birds more frequently because they are more plentiful than small mammals.

Although not on the critical list as a species, numbers have declined by a third in the last 30 years, said a spokesman for the Royal Society for the Protection of Birds.

"It's absolutely fantastic that Artisan is prepared to change its plans for the birds' sake," he said.

"We are aware that birds sometimes nest in the most inappropriate places so it's always great to hear that people will put themselves out to accommodate them."

Experts believe that the birds will all have flown by the end of July, delaying Gary's new showroom opening by just two or three weeks.

But it might not be the last he sees of them. According to the RSPB, the birds often use the same nest site in successive years - with some sites used for decades.