Foreign Secretary Dominic Raab has rejected suggestions that rapid testing alone could be used to release travellers to the UK from quarantine.
On Wednesday Government adviser and immunologist Professor Sir John Bell said data had shown from January that testing could be used to release travellers to the UK from self-isolation on arrival.
Responding on why testing could not be used immediately to ease international travel restrictions, Mr Raab told Sky News: "We are doing daily testing, but I think the answer to your question ‘why do it now not in say, two-and-a-half weeks’ time?’ is we know and we can project how many people broadly we’ll have double vaccinated and that is the level of reassurance we want to get to.
"I know it has been frustrating, I know it has been an inconvenience, there’s been lots of things in this pandemic that have been inconvenient.
"But the truth is the whole tide – whether it is domestic restrictions, international – is going in the right direction of opening but we do need to just be careful, make sure we are doing it at the right time."
On a more positive note, it appears more countries are set to be shifted onto a more favourable list.
Travel countries on the red, green and amber list
Mr Raab told Sky News: "I can’t rule things out but the Joint Biosecurity Centre (JBC) and the Government will decide.
"But they’ll make that decision next week in terms of the traffic light system for all the relevant countries.
"I think personally feels like the momentum forward is positive, because as I say because the double vaccination, reaching 70 per cent of the adult population in this country (see the graphic below on how your area is faring).
How many people have been vaccinated?
"We’ve done the job we had to do domestically, and as we see other countries catch up if you like. I think we’re increasingly confident that more countries will go to on the either on amber or on to green."
The Foreign Secretary also said the Government "cannot guarantee" that US and EU travellers will not try to show fake vaccination certificates.
He told BBC Radio 4’s Today programme: "We can’t guarantee that some people might not do it. I think it is highly unlikely.
"The point here is that, with both the European countries and the US, we are talking about high-trust countries with whom we have not just an intuitive level of high trust, we have active co-operation, so we know that we can straighten out any discrepancies we might come across pretty quickly."
Mr Raab said there is a "double lock" of written certification and proof of US residency for American travellers, which he said could allow "further checks if there is any suspicion of fraud".
He added: "Both domestically with our rollout but also internationally we want to open up, we want to move the country forward, but we want to do it irreversibly and we need to take solid, surefooted steps forward.
"We feel this is a modest opening up of international travel but one that has the reassurances that we can take further steps forward as we build confidence in the system."