England are preparing to name an entirely new squad to face Pakistan in the Royal London one-day series after a major Covid-19 outbreak hit the camp.

The entire squad took PCR tests in Bristol on Monday following the third ODI against Sri Lanka, with three players and four members of the backroom team returning positive results.

The remainder of the group were identified as close contacts, forcing all parties into a period of isolation from July 4, in line with public health guidelines.

An unprecedented development such as this could easily have put the three-match series in jeopardy, but the England and Wales Cricket Board moved quickly to ensure the fixtures go ahead.

The ECB resolved to put together a hastily-convened shadow team, captained by the returning Ben Stokes, and was preparing to announce names on Tuesday morning – barely 24 hours before the first game in Cardiff.

Stokes, who has been pulled out of Durham's LV= Insurance County Championship match against Warwickshire, had been left out originally in a bid to manage his comeback from a finger operation. That plan, along with so many others, is now in tatters. Head coach Chris Silverwood, who had been planning to take the series off, is cutting short his scheduled break to retake command.

The current round of championship matches are highly likely to be disrupted on a mass scale as players are rounded up for unexpected international duty.

ECB chief executive officer Tom Harrison accepted the development was a natural consequence of a calculated decision to move away from the strictly enforced bubbles that were in evidence last summer.

While successful – there were no positive cases at all during a full programme of men's fixtures – they were also felt to place too great a burden on the mental health of those involved for long periods.

"We have been mindful that the emergence of the Delta variant, along with our move away from the stringent enforcement of bio-secure environments, could increase the chances of an outbreak," said Harrison.

"We made a strategic choice to try to adapt protocols, in order to support the overall well-being of our players and management staff who have spent much of the last 14 months living in very restricted conditions.

"Overnight we have worked swiftly to identify a new squad, and we are grateful to Ben Stokes who will return to England duties to captain. We also recognise the impact this news will have on our first-class counties and their men's playing squads and thank them, along with our partners Sky and Royal London, for their ongoing support in dealing with this pandemic."

The new players and staff who are drafted in will need to submit negative PCR tests and complete "bridging protocols" before joining the squad in Cardiff.

That match will take place in front of a 50 per cent capacity crowd, with the second game at Lord's on Saturday representing cricket's first 100 per cent crowd since the pandemic began. The series then concludes at Edgbaston and, as it stands, no changes are anticipated to the venues or admittance numbers.