Fewer than one in 20 MPs have signed a Commons motion demanding tough changes to the ban on hunting.

On the eve of a crucial court test case involving West huntsman Tony Wright, which will determine what happens to other prosecutions, an MP is canvassing support to changing the law.

John McDonnell, one of the architects of the 2005 Hunting Act, has tabled a Commons Early Day Motion (EDM) saying "there is mounting evidence that hunts are avoiding the law".

It claims huntsfolk "by various devices are continuing the barbaric practice of hunting foxes down to a bloody kill and claiming that such kills are accidental".

Labour MP Mr McDonnell is calling on the Government to amend the Act to include a "reckless behaviour clause" which he says would prevent the abuse of the spirit of the legislation.

He tabled the EDM on December 4 after admitting in an interview about the issue: "It took a long time. There was a lot of discussion. We thought we got it right, but we clearly haven't in this instance."

But, so far, just 28 other MPs have added their names, including former Labour Minister – and Oscar-winning actress – Glenda Jackson, and Graham Stinger, who was also in the Government under Tony Blair.

Some Liberal Democrats have also signed, but not ex-Home Office Minister Ann Widdecombe, one of the few Tories to oppose bloodsports, who has previously said the law is enforceable.

Stroud Labour MP David Drew has supported it, along with Bristol West Lib Dem Stephen Williams, who was not an MP when the Hunting Act was passed, but says he would have voted for it.

He said he found it "immensely frustrating" when people got away with behaviour that breached both the letter and the spirit of the law, and that an amendment would give clarity.

Mr Williams said there was "probably little chance" of the Government taking action before the next General Election, which will be within 18 months, but Labour may think that doing so would be popular.

The Countryside Alliance (CA) said the issue should not be top of the agenda in a recession and the fact that just 29 MPs had backed the EDM showed it was not.

"The Government, and rightly so, has higher priorities at the moment and that is reflected by only 29 MPs signing," a spokesman said.

The group said the EDM was an admission by Mr McDonnell and other MPs they spent 700 hours of Parliamentary time "on a piece of legislation that has failed completely to do what they wanted it to do.

"But others say it is a fine piece of legislation, it just needs enforcing better – there are different messages coming out and they appear to be in disarray."

The CA claims the anti-hunting movement is split. It said amending the Act is "like the Pharaohs viewing the finished Pyramids and deciding they would prefer them square", and added the only answer is to repeal it.

The International Fund for Animal Welfare said more police are needed out in the fields, along with more monitoring, and advises anti-hunt supporters to write to their MP demanding the law is properly enforced.

Controversy over hunting will increase tomorrow when a High Court hearing begins on the case of Tony Wright, the first huntsman to be prosecuted over the Act.

All hunt prosecutions, including state ones led by the Crown Prosecution Service and private ones taken by the League Against Cruel Sports, have been frozen pending the outcome.

The three-year-old case involving the Exmoor huntsman will set a precedent for the way the law is dealt with in court – although no decision is expected until the New Year.