Boris Johnson has been warned that a further relaxation of restrictions over Christmas could trigger another wave of coronavirus infections. NHS Providers, which represents health trusts in England, has told the prime minister in a letter to exercise 'extreme caution' when making the decision to move any areas into a lower COVID-19 tier. The coronavirus tier system is due to be reviewed on Wednesday, two weeks after it was first imposed following England's national lockdown in November. NHS bosses say areas which need to be moved into Tier 3 should be done so 'as soon as this is needed, without any delay'. It comes ahead of a UK-wide relaxation of social distancing rules for Christmas, allowing up to three households to get together in homes and places of worship between 23-27 December. While NHS Providers stopped short of calling for this relaxation to be scrapped, the letter did ask the prime minister to set out the risks of increased contact over Christmas. Speaking to Sky News, NHS Providers CEO Chris Hopson said health workers are 'really worried', adding that due to a surge in COVID-19 patients and a rise in infection rates, hospitals are facing a difficult period. 'Any extra social contact equals virus spread,' he said. 'We all want to get together, but we need to ensure we look at the evidence. Although we've made some good progress… the reality is the progress we've made as a whole is at the lowest end of expectations. 'We've got to keep going with these tough restrictions over winter… we cannot take risks'. NHS bosses are concerned that the UK could follow in the footsteps of the US, which experienced record coronavirus-related hospitalisations and infections following Thanksgiving, when millions of families got together to celebrate. A government spokeswoman said ministers will not 'hesitate' to take actions where needed, adding that decisions are made based on the latest available data. 'We have introduced strengthened local restrictions to protect the progress gained during national restrictions, reduce pressure on the NHS and ultimately save lives,' the spokeswoman said. 'On top of our record NHS investment, this winter we are providing an extra £3bn to maintain independent sector and Nightingale hospital surge capacity and a further £450 million to upgrade and expand A&Es.' - Sky News