The message from Network Rail and train operators is "do not travel to or from London" at the weekend, beginning Saturday, February 29. In Cambridgeshire, the line between Peterborough and London King's Cross will be closed but trains will still run between King's Lynn and Letchworth Garden City via Cambridge. It is all part of a £1.2 billion investment to "improve rail infrastructure" and will cause chaos across most parts of the UK, especially in London. No train services will run between Biggleswade or Letchworth Garden City and King's Cross, St Pancras International or Moorgate stations Passengers are urged not to travel to or from London King's Cross or St Pancras International on either Saturday, February 29 or Sunday, March 1. Over the weekend, Network Rail engineers will test new signalling equipment at Stevenage station as part of work to construct a new platform there, which will allow more train services to run. The testing of the signalling system can only be done safely when no trains are running, so the line between Biggleswade and London King's Cross will be closed. There will also be no Great Northern or Thameslink services between Letchworth Garden City and London King's Cross or London St Pancras International, and no services in or out of Moorgate, including via Hertford North. A spokesman for Govia Thameslink Railway said: "Passengers are advised to travel on either Friday, February 28 or Monday, March 2, however those travelling on these days should book in advance and reserve a seat where possible. "If passengers absolutely must travel over the weekend, they should allow significantly more time for their journey, as they will need to use the limited bus replacement services or alternative routes, which will be very busy." Ed Akers, principal programme sponsor for Network Rail, said: "We know that there have been numerous changes to services to and from London this year and we apologise for any inconvenience which this has caused. "We understand that there's never a good time carry out upgrade work on this scale. The work taking place on Saturday and Sunday is absolutely vital to move the scheme forward and we would urge passengers not to travel to and from London on the affected routes this weekend. "This work will now not impact on services until June and I would like to thank passengers for their continued patience whilst we work on the upgrade, which will bring huge benefits to passengers when completed." A spokesperson for train operators along the route, said: "This weekend, significant work by Network Rail will mean widespread changes to services on the East Coast Main Line into London King's Cross, as well as between Letchworth Garden City and St Pancras, including the Moorgate Line via Hertford North. "We urge passengers to follow the travel advice issued and not to travel to or from London on these routes this weekend. Passengers should travel on alternative dates. "We would like to thank all passengers for their patience and we look forward to them reaping the rewards when this project completes."