The Royal Navy patrol vessel HMS Mersey has been deployed to the Channel to help deal with people attempting to cross to the UK from France, ministers have confirmed.

The move came after a formal request for military assistance from the home secretary, Sajid Javid. The deployment will be financed by the Home Office.

“My focus continues to be on protecting the UK border and preventing loss of life in the Channel,” Javid said, adding that the measure would be temporary to plug the gap while two Home Office vessels make their way to the area.

“It is vital that we are working on all fronts to tackle this ongoing situation and I am grateful to Border Force and other agencies for the tireless work they have done in response to this activity.”

The defence secretary, Gavin Williamson, said: “The professionalism of the Royal Navy means the crew have been able to immediately divert from routine operations to help prevent migrants from making the dangerous journey across the Channel.”

Javid has declared the attempts by 539 people to cross the Channel in small boats over the course of last year – the majority in the final three months – a “major incident”. He has been criticised for questioning whether the people making the crossing were “genuine” asylum seekers and for making what experts said was an unlawful threat to try to make it more difficult for people to gain asylum in a bid to deter future attempted crossings.

The shadow home secretary, Diane Abbott, has said the comments were part of a Conservative “obsession with maintaining a hostile environment” for refugees and people who are migrating, evoking the language surrounding the Windrush scandal. “Suggesting that the British government would deny legitimate asylum claims is not only a disgrace but a breach of the 1951 refugee convention,” she said.

Her Labour colleague and the chair of the home affairs select committee, Yvette Cooper, added: “Asylum claims have to be determined according to the law and the circumstances of every individual case, not as an arbitrary political decision supposedly to deter others. The home secretary knows this, so to suggest otherwise is completely wrong.”

Javid’s response to the issue also led Abbott to speculate about his motives on Thursday. “I think Sajid Javid is virtue-signalling to the media. It’s all about the Tory leadership,” the Financial Times quoted her as saying on Thursday. “The numbers involved are not huge compared to the number of people turning up on the coast of Greece during the last crisis [of 2015-16].”