Almost 16,000 more animals were abandoned last year than in 2007, according to the RSPCA, who warned that pet owners are struggling to make ends meet in times of economic hardship.
The charity said 40,595 animals were abandoned in 2011, compared with 24,638 in 2007, a near 65% increase. Over the same period, and despite efficiency savings, the charity's running costs have risen 8% from £111 million to £120 million.
Despite the recession being over, animals are still facing "dark times", according to RSPCA chief executive Gavin Grant. He added that with the charity having to do more to help animals in need, they are "struggling to cope", and called for people to donate to the RSPCA.
The charity said it is finding it harder to find new homes for abandoned pets, with 12,711 dogs rehomed in 2011, compared with 16,659 in 2009. The RSPCA rehomed 29,880 cats in 2011, less than the 36,070 two years before. Both species are taking longer to rehabilitate and rehome than a year ago, meaning their average cost of stay is also rising.
The average stay for a dog in the year so far is 59 days, five more than last year, and their average cost of stay has risen from £810 to £885. Cats have also averaged stays of 59 days this year, four more days than in 2011, and the average cost of their stay has risen to £554.60 from £517.
The charity said it is currently responding to more than 25,000 calls a week from the public and has seen a 23.5% rise in cruelty convictions in the last five years. The first nine months of this year alone have seen 1,176 cruelty convictions involving work by the RSPCA, a 6% rise on the same period in 2011, which saw 1,108 convictions.
As the number of animals in need grows, welfare expenditure by the RSPCA - which relies entirely on public donations - is already exceeding forecasts set for 2012. The charity said it predicted a further 6,000 dogs and cats will be abandoned between now and the end of the year at a cost of nearly £5 million.
Mr Grant has called for emergency help from the nation's animal lovers. He said: "The recession may be over but these are very dark times for its silent victims - the animals. They have never needed our help so desperately.
"Preventing cruelty and helping the animals most in need are the RSPCA's absolute priorities but the number of abused and abandoned animals is soaring. At the same time, we have more animal abusers to investigate, prosecute and hopefully prevent from hurting animals than anyone can remember.
"This is a real crisis and despite the immense dedication of our staff and volunteers, we are struggling to cope. We really need our country's animal lovers to step forward and open their hearts, homes and purses in these extremely difficult times."