By Nina Chestney LONDON (Reuters) – Octopus Energy Ltd is now the fifth biggest power supplier in the UK after taking on new customers which increased its revenues last year following the collapse of smaller suppliers. Octopus reported energy supply revenues of 1.9 billion pounds ($2.6 billion) to April 30 2021, versus 1.2 billion in the same period a year before, as its customer base rose to 2.1 million, it said in full-year results on Saturday. The privately held company, part of the Octopus Energy Group, now has more than three million customers, ranking it the fifth largest energy retailer…