GlaxoSmithKline (NYSE: GSK) faces at least four U.K. lawsuits over its Avandia diabetes drug amid claims it’s linked to an increased risk of heart attacks and congestive heart failure.

The potential number of claims against the U.K.’s biggest drugmaker may increase, said Daniel Slade, a lawyer at Manchester firm Express Solicitors, who represents consumers in the four suits and has a further 15 clients.

“We expect the number of claims to increase as there are potentially thousands of people out there who took Avandia in the U.K.,” Slade said in a telephone interview today. “Hopefully these claims will lead to more careful studies and checks on drugs that are widely marketed.”

Glaxo has said it paid more than $3 billion to settle U.S. federal and state government claims that it illegally marketed Avandia, once the world’s best-selling diabetes pill, and other medications.

According to estimates by Bloomberg news service, individual Avandia settlements in the U.S. will be around $57,000.

Slade told The Guradian newspaper that he was “very disappointed” by GSK’s decision.

“It is very disappointing,” said Slade. “We anticipate that these claims do have a good prospect of success, but they still have to prove their case in the UK with suitable evidence. They are tasked with having to produce that evidence, including medical expert opinion. It is a burden one would have thought they might not have to go through.”

David Daley, a spokesman for Glaxo, said that while the company can’t comment on specific cases, it has “every sympathy for people with health complications associated with diabetes.”

“We continue to believe that the company acted appropriately and responsibly in its management of Avandia,” Daley said.

Glaxo indicated to Express Solicitors that it intends to fight the claims, filed in Manchester, England, setting aside 600,000 pounds ($946,200) in litigation costs for one case, Slade said.

“Even though a settlement was reached in the U.S. to settle lawsuits, it seems GSK wishes to put up a fight in the U.K.,” Slade said.

GSK operates its North American headquarters in RTP.

[GSK ARCHIVE: Check out 10 years of GSK stories as reported in WRAL Tech Wire.]

(Bloomberg contributed to this report.)