Oct 27 (Reuters) - Britain’s GSK beat analysts’ expectations for third-quarter earnings on Wednesday and raised its outlook for annual profit ahead of a planned split next year. The company now expects 2021 adjusted earnings per share to decline by between 2% and 4% at constant exchange rates, excluding any boost from its COVID-19 offerings. It previously expected profit to fall by mid-to-high single digit percentages. Reporting by Pushkala Aripaka in Bengaluru and Ludwig Burger in Frankfurt; editing by Jason Neely