A delay in deliveries from India and the need to retest a batch of 1.7 million doses is behind an expected shortfall in coronavirus vaccine supply in April, Matt Hancock has said.

The Health Secretary told MPs that a partnership with the Serum Institute of India is one the UK “can be proud of”, despite a delay in deliveries of the AstraZeneca vaccine from its plant.

NHS England told health leaders on Wednesday to expect a significant shortfall in vaccine doses from March 29 for about four weeks.

It said people under 50 should not be booked in for first appointments unless they fell into a higher priority group, such as being clinically vulnerable.

The move means the under-50s could now have to wait until May to get a vaccination, despite doctors having planned to start on that group in April, Martin Marshall, chairman of the Royal College of GPs has said.

Mr Hancock told MPs: “We have a delay in the scheduled arrival from the Serum Institute of India.

“Now, I want to put on the record my gratitude to the Serum Institute of India for the incredible work that they’re doing producing vaccine not just for us in the UK, but for the whole world.”

Downing Street did not deny, however, a suggestion from the head of the Serum Institute of India that the Indian government was temporarily blocking exports of the AstraZeneca vaccine.

Its chief executive Adar Poonawalla told The Telegraph: “It is solely dependent on India and it has nothing to do with the SII (Serum Institute of India). It is to do with the Indian government allowing more doses to the UK.”

The Prime Minister’s official spokesman said: “I would point back to what the Serum institute have said and the fact that they are one of the manufacturers of the Oxford/AstraZeneca vaccine.

“We produce it here in the UK and it’s produced elsewhere as well so we will continue to work with the manufacturers of the vaccine.”

Asked if the UK Government is in talks with the Indian government, he said: “We’re in constant contact with other governments around the world.”

In the Commons, Mr Hancock said that a batch of 1.7 million doses of vaccine had been delayed in the last week due to the need to retest its stability.

“Events like this are to be expected in a manufacturing endeavour of this complexity and this shows the rigour of our safety checks,” he said.

Mr Hancock said second doses for people would be prioritised in April, and there would also be some first doses, but did not make clear for which groups.

“There will be no weeks in April with no first doses,” he said.

“There will be no cancelled appointments as a result of supply issues – second doses will go ahead as planned.”

It comes as Scotland’s First Minister Nicola Sturgeon said Scotland will have 500,000 fewer coronavirus vaccine doses over the next month than anticipated.

The Government has stated that the UK is still on track to offer a first dose to all adults by the end of July.

Earlier, Prof Marshall, chairman of the Royal College of GPs, said news of constraints in supply was “disappointing” and “a bit of a setback”.

He said: “The impact of this shortage of supplies will happen on the group that we were hoping to start on in April, which is the people under the age of 50 without any pre-existing conditions, who are now going to have to wait until May.”

Cabinet minister Robert Jenrick also conceded that the rollout of vaccines would be slower than expected because of the shortage, while Professor Adam Finn, a member of the Joint Committee on Vaccination and Immunisation (JCVI), said vaccination of those aged under 50 “may kick off slightly later than we’d optimistically hoped”.

However, Northern Ireland has suggested it may still be able to start vaccinating people in their 40s from mid-April.

Conservative former health secretary Jeremy Hunt questioned Mr Hancock over suggestions that vaccine exports could be blocked by the EU, following comments by the head of the bloc’s executive, Ursula von der Leyen.

Mr Hancock replied it was “vital that we all work together”, adding: “These supply chains for the manufacture of these vaccines cross borders.

“They are often global supply chains and it is vital that we work together to deliver them and there is a need for that co-operation and there is of course a need for all countries to respect contract law.

“That is the basis of international trade and I’m sure that the European Union will live up to the commitments and statements that it has made, including president von der Leyen herself, who has said that there should not be restrictions on companies when they are fulfilling contractual responsibilities.

“Of course there should not and we fully expect those contracts to be delivered on because there are very significant consequences to breaking contract law.”

Mr Hancock told MPs that vaccine supply issues will have “no impact on the road map” out of lockdown, as he confirmed that supplies of the Moderna vaccine are due in the coming weeks.

“To any member of the public who is watching, what I would say very clearly is that the vaccination programme is on track to meet the targets that we have set out,” he said.

“We are on track for the dates in the road map and there is no impact on the road map from the changes to vaccine supply that we’ve been detailing in the last 24 hours.”