A Downing Street spokesperson said the two River-class vessels will continue to "monitor the situation as a precautionary measure".
The two ships began deploying last night, amid a protest by French fishing vessels at the port of St Helier over the lack of access.
French fishing vessels gathered near the harbour on Thursday morning, with some crews setting off flares.
A Ministry of Defence (MOD) spokesman said the River-class warships are "strictly a precautionary measure" and their presence "has been agreed with the Jersey government".
France's maritime minister Annick Girardin warned on Tuesday the country was ready to take "retaliatory measures", after accusing the Channel Island of dragging its feet over issuing new licences to French boats.
Prime Minister Boris Johnson spoke to Chief Minister of Jersey, Senator John Le Fondre, and the Minister of External Affairs, Ian Gorst, on Wednesday, and "underlined his unwavering support" for the island.
A Downing Street spokesperson said on Wednesday: "The Prime Minister and Chief Minister stressed the urgent need for a de-escalation in tensions and for dialogue between Jersey and France on fishing access.
"[The Prime Minister] said that any blockade would be completely unjustified.
"They agreed the UK and Jersey governments would continue to work closely on this issue."
An MOD spokesperson added that HMS Severn and HMS Tamar were "deploying to Jersey to conduct maritime security patrols".
"This is a strictly precautionary measure and has been agreed with the Jersey government," they continued.
What are the Navy's offshore patrol vessels?
Royal Navy offshore patrol vessels (OPV) protect the UK's interests at home and abroad, safeguarding territorial waters, protecting fishing stocks and performing constabulary duties.
All eight River-class vessels are based in Portsmouth, and consist of two generations – Batch 1 ships, and the newer Batch 2s.
HMS Severn, a Batch 1 ship, was re-commissioned into the Royal Navy last summer, nearly three years after she was decommissioned.
Watch: In 2016 we spent time on board HMS Severn to learn more about the Royal Navy's Fishery Protection Squadron.
She only set sail from Falmouth this week, ahead of her final big maintenance period before her next overseas operations to the Asia-Pacific, before being deployed to Jersey.
What has led to the tensions?
The UK and Jersey have already criticised France for making "disproportionate" threats after Paris warned it could cut off electricity to the island.
The row has come after the island implemented new requirements under the terms of the UK-EU trade deal for boats to submit evidence of their past fishing activities in order to receive a licence to carry on operating in Jersey waters.
Jersey receives 95% of its electricity from France through three undersea cables.
French maritime minister Ms Girardin told the French parliament that it gave Paris the "means" to act against the island if the issue could not be resolved.
"Even though I am sorry that it has come to this, we will do so if we have to," she said.
Minister of External Affairs Mr Gorst told the BBC Radio 4 Today programme: "This is not the first threat that the French have made to either Jersey or the United Kingdom since we are into this new deal.
"It would seem disproportionate to cut off electricity for the sake of needing to provide extra details so that we can refine the licences."
On Wednesday Mr Gorst held talks with Marc Lefevre, the president of the La Manche region of northern France, on the "difficult set of issues relating to fishing licences".
"There are a number of important matters which we will continue to work through," he said.
He added that the island was not seeking to bar boats which had historically fished in Jersey waters and insisted the dispute could be resolved amicably.
Of the 41 boats which sought licences under the new rules last Friday, all but 17 had provided the evidence required, Mr Gorst said.
"The trade deal is clear but I think there has been some confusion about how it needs to be implemented, because we absolutely respect the historic rights of French fishermen to fish in Jersey waters as they have been doing for centuries," he said.
"I do think a solution can be found. I am optimistic that we can provide extra time to allow this evidence to be provided."
He said the Jersey government was now seeking permission from London and Brussels to speak directly with the French fishermen concerned to resolve the issue.
Cover image: Alamy.