n a packed Westminster debate, Conservatives accused the charity of becoming too "political" for spending hundreds of thousands of pounds prosecuting a high-profile hunt.
The RSPCA has been asked to review its prosecution policy by the Charities Commission, after it spent £326,000 taking the Prime Minister's local hunt to court.
Sir Edward Garnier, a former solicitor general, said the prosecution costs of the Heythrop hunt case were a "misjudgement".
"It seems to me that if they continue to prosecute at such huge expense and in such a disproportionate way they will be open to public criticism," he said.
Sir Edward said there is a danger of the RSPCA "using the weapon of the state prosecution for political campaigns".
He said the charity should continue investigating animal welfare issues but they should, like the police, hand the evidence over to the "dispassionate" Crown Prosecution Service.
Some MPs called for more oversight of the RSPCA's prosecution arm. However, the Government admitted it has no control over the RSPCA because the charity has no official prosecuting role and the hunting lawsuits are brought privately.
Simon Hart, a Tory MP for Carmathen and West Pembrokeshire, said the charity's prosecuting role needs to be monitored given its "political and commercial activities".
He said there is a "gulf between the very good activity of inspectors on the ground whose principal concern is animal welfare" and the leadership whose principal concern seems to be "animal rights"
Glyn Davies, a Conservative MP for Montgomeryshire, said the RSPCA is likely to lose support for deviating from its core role.
"In my mind the RSPCA was always an animal welfare body, that's how I always saw it. But I must admit I'm finding it more to be an animal rights body."
He added: "I want my RSPCA back."
A raft of Labour MPs and Caroline Lucas, former leader of the Green Party, defended the RSPCA as no public body has the expertise or resources to carry out the work the charity currently does.
Ms Lucas said prosecuting the Heythrop hunt was right because "upholding the law is not a political act". Others questioned the motivation of Conservatives for launching an attack on the animal charity.
Paul Flynn, Labour MP for Newport West, said the Conservative MPs were criticising the RSPCA's role as a prosecutor as a "smokescreen" to stop lawsuits against illegal hunting.
"(Are they) saying all lawbreakers should be prosecuted unless they are rich, powerful and Tory?" he said.
Cheryl Gillan, Tory MP for Chesham, also broke ranks with her party to congratulate the RSPCA for its work, including its prosecution of the hunt.
The Government said there could be no official control over the RSCPA by legal inspectors as the charity has "no special role as a prosecutor".
Dominic Grieve, the Attorney General, said it is an "ancient right" for right individuals and groups to bring private prosecutions, which remains "fundamental and important".
Following the debate, charity groups defended their ability to bring private prosecutions.
Ben Kernighan, deputy chief executive of the National Council for Voluntary Organisations, said using the law is an "entirely legitimate and often very effective way for charities to pursue their aims".
"There are a number of safeguards in place to ensure private prosecutions are brought proportionately and appropriately, as the Attorney General has said," he said.
A spokesman for the RSPCA said the charity takes its "responsibilities as a prosecuting body extremely seriously and will continue to do so".
"We are as committed to our mission, to promoting compassion to all creatures and prevent cruelty, as ever," he said.
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