SCOTLAND'S female panda is showing encouraging signs she may be pregnant, raising the prospect of a £50 million boost to the economy, according to experts.

Keepers at Edinburgh Zoo are hopeful Tian Tian could give birth to the UK's first panda cub within weeks after they noted changes such as a lack of appetite, restlessness and nesting behaviour like making a bed of straw.

Experts are being cautious as it has not been possible to carry out an ultrasound on the panda, which arrived from China in December, and the symptoms may be that of a pseudo-pregnancy, but they said it looks "promising".

The birth of a cub - or cubs -could bring £50m to the Scottish economy over the next decade through tourism and visitor spending, according to analysis from Scottish Enterprise,

Henry Nicholls, author of The Way of the Panda: The Curious History of China's Political Animal, said yesterday: "A cub will usually rejuvenate gate receipts, recreating the excitement experienced during the first heady days of a loan. It'll be a question of capacity. How can the zoo satisfy all the new fans who want to see a cub - or cubs?"

Tian Tian was artificially inseminated after two failed attempts to mate with the zoo's male, Yang Guang. Tian Tian was also inseminated with frozen semen from another panda called Bao Bao who lived at Berlin Zoo.

Conservation geneticists will use blood samples from any cub to establish who is the father. If twins are born, they could have different parentage.

Iain Valentine, director of the zoo's panda project, said it was "hugely exciting" because a panda has never been born in the UK.

"Since the artificial insemination, which took place in April, we've been monitoring hormones and we've also been monitoring an acute protein in her urine.

"So we've got to a point where the profile she has been building up over the last few months is looking quite promising. Now we have taken another step in that the progesterone levels have now increased, which means that we are into the last 40 to 55 days of either pregnancy or pseudo-pregnancy.

"On top of all that, all of her behaviours are now shifting as well, so the overall picture is looking quite good."

Royal Zoological Society of Scotland (RZSS), the conservation charity that owns Edinburgh Zoo, has been working with international experts to determine whether Tian Tian is expecting a cub.

Scientists have been using new protein-analysis techniques ­developed by Tennessee's Memphis Zoo in the US.

Urine samples are flown away each week for testing by Dr Martin Dehnhard of the Leibniz Institute for Zoo and Wildlife Research in Berlin, one of the experts who helped carry out the panda's artificial insemination. A second rise in progesterone hormone levels was detected in Tian Tian on July 15 and confirmed on Wednesday.

Results suggest the profile of a pregnant panda that will carry to full term but the zoo cautioned that the method is relatively new and so not definitive. Mr Valentine said that over the next two or three weeks a better indication will emerge as the profile of the hormones and protein is built up. He added: "Tian Tian still may be experiencing a pseudo-pregnancy, so it is important to remember that. There is still a need to just watch and wait while continuing to monitor her hormone levels."

"Confirming a female panda's pregnancy is never straight-forward and we would encourage people to try not to get too excited just yet.

"Further hormone results will be available roughly by mid-August that will add to the picture. If Tian Tian is not pregnant, specific hormone levels should drop back down to zero."

Any cub or cubs would be born in late August or early September. Giant pandas start to show signs of labour 24 hours in advance.

If the pregnancy is confirmed, an expert from China will fly over before the birth and stay at Edinburgh Zoo for the first few months of the cub's life.