LONDON (Reuters) - Hospira (>> Hospira, Inc.) has successfully overturned two patents on Roche's (>> Roche Holding Ltd.) top-selling breast cancer drug Herceptin in Britain, clearing the way for it to launch a cheaper copycat version in the country.

A ruling handed down by the High Court in London on Thursday determined that both the 115 patent and the 455 patent on the drug were invalid.

Herceptin, an injectable antibody-based biotech drug, had worldwide sales of 6.08 billion Swiss francs (4.1 billion pounds) last year.

U.S.-based Hospira has pioneered the development of so-called biosimilar versions of biotech drugs. Unlike conventional chemical medicines, these biological drugs are complex to make and copies can only ever be similar to the original product rather than exact replicas.

Hospira recently launched the first antibody biosimilar in Europe, called Inflectra, which is a copy of Johnson & Johnson's (>> Johnson & Johnson) and Merck & Co's (>> Merck & Co., Inc.) Remicade drug for rheumatoid arthritis.

(Reporting by Ben Hirschler and Kate Kelland. Editing by Jane Merriman)