Merck & Co's cancer drug Keytruda, which works by boosting the immune system but has yet to be licensed in Europe, is the first medicine to be made available to patients in Britain under a new early access scheme.

The Medicines and Healthcare Products Regulatory Agency said on Wednesday that the treatment had been cleared to treat adults and children from 12 years of age with advanced melanoma, the deadliest form of skin cancer, after other drugs had failed.

Keytruda, or pembrolizumab, was accepted under the scheme based on the significance of early study findings and unmet medical need. It had already received a "promising innovative medicine" designation in Britain in October 2014.

The British initiative, which has similarities with a U.S. scheme that has accelerated the development of so-called "breakthrough" medicines, follows criticism that Britain's state-run healthcare system is too slow to adopt new treatments.

The new early access program is funded by drug companies.

While Keytruda is already approved in the United States, Merck's application for marketing authorization in Europe is still under review.