Nov 8 (Reuters) - Finnish insurer Sampo reported forecast-beating quarterly earnings on Wednesday, citing continued improvement in the pricing environment in the British motor insurance market and higher interest rates supporting investment income.

The company's third-quarter profit before tax rose 14% to 391 million euros ($417.6 million), above analysts' estimate of 312 million in a poll by Vara Research.

It was Sampo's first earnings report since it spun off life insurance unit Mandatum, which debuted on Nasdaq Helsinki on Oct. 2. Before that, Sampo had labelled Mandatum as discontinued operations from the end of March.

The partial demerger marked the completion of Sampo's long-planned shift into a pure-play property and casualty (P&C) insurer. ($1 = 0.9363 euros) (Reporting by Marta Frckowiak in Gdask; editing by Milla Nissi)