Travel agents have told customers to wait until at least June before flying abroad, with holidaymakers running the risk of losing money and facing unknown testing costs.

The news comes as On The Beach, an online travel agent, announced it was booking no holidays this summer until the outlook was more certain.

With countries including Portugal open for business from May 17 prices for flights and accommodation have spiked, according to Nick Lee of North Walsham's Broadland Travel Worldchoice.

But customers will get a much more certain - and potentially cheaper - deal if they hang on to their sunhats a little while longer.

"If a customer calls me and says they want to be in Portugal this month I strongly advise them to hold off until June. We saw how quickly things changed last year and June gives us more certainty," he said.

"I am less concerned more generally than I was last year. Firstly because I know who to book with that guarantees refunds but also because the procedures to carry that work out is now far more transparent.

"By then I suspect we'll also see Greece on the green list, which is where I think we'll see much better deals. I priced up a Portugal holiday for a family and it came to £3,000. With the deals and the greater availability of accommodation coming in from June they'd pay half the price if they held off."

He was echoed by Rebecca England of Attleborough Travel, who said: "Not only is it uncertain which countries will stay on the green list the costs around testing are so variable.

"It can be anywhere between £20 and up to £75 which obviously is a massive price difference if you're booking for a family of four and we can't confirm that on cost straight away.

"I think Greece will be incredibly busy. Usually you'd expect Turkey to be on that cheaper end of the spectrum but with that being a red-listed country I think there will be a lot of uncertainty travelling there.

"I think because of that uncertainty a lot of people are still booking in the UK. I adjusted my sights slightly to both domestic and foreign holidays because that was where I was still seeing a lot of demand for this year."