Downing Street has defended Britain's response to the Syrian refugee crisis after it was condemned as "deeply inadequate" by more than 300 lawyers, including a former president of the Supreme Court.

Lord Phillips of Worth Matravers, the first head of Britain's highest court, three other former law lords and the former president of the European Court of Human Rights Sir Nicolas Bratza were among the signatories to a statement denouncing an offer to house 20,000 refugees over five years is "too low, too slow and too narrow".

Five retired Lords Justices of Appeal, the former Director of Public Prosecutions Lord MacDonald, Lib-Dem peer Lord Carlile of Berriew QC and more than 100 Queen's Counsel, are also on the list.

However the Prime Minister's official spokeswoman insisted the UK could be "proud" of its response to the crisis, which included £1.1 billion in assistance to support refugees in the region, making it the second largest bilateral donor.

"A lot of people recognise that we are substantially increasing the numbers of refugees that we are resettling and they recognise too that the long-term solution to this problem lies in our actions to find a solution in Syria and helping people there and in the region to be able ultimately to return home," the spokeswoman said.

The statement published at www.lawyersrefugeeinitiative.org, says: "We consider that the UK Government's offer to resettle 20,000 of the most vulnerable Syrian refugees from camps in the Middle East, spread over five years, is too low, too slow and too narrow."

It comes after Oxfam last week accused the Government of not taking its "fair share" of Syrian refugees.

For Labour, shadow home secretary Andy Burnham said the lawyers' statement was a "serious intervention" which ministers could not afford to ignore.

"While it is right for Britain to stay outside of any formal EU quota scheme, the Prime Minister and Home Secretary should reach out to counterparts across Europe and take a fair share of refugees this year, as well as increasing support to agencies in war-torn nations," he said.

The SNP's Europe spokesman Stephen Gethins said: "The UK Government must cooperate with our European neighbours to find a solution to one of the biggest humanitarian crisis of our time. The scale of the refugee crisis is one we haven't seen since World War II."

Sir Stephen Sedley, a signatory to the statement and a Lord Justice of the Court of Appeal until he retired in 2011, said: "It is within the UK's power to curtail the lethal boat traffic by enabling refugees from countries such as Syria and Iraq to travel here lawfully in order to apply for asylum.

"As a stable and prosperous country, we can do better than this."