Based on the increase in fuel consumption and the screeching noise that you experienced when the car was cold, it may be that while the car was stood idle an engine component or components have become partially seized, such as an auxiliary belt or tensioner. This would account for the noise, and also an increase in friction of the engine components could cause increased fuel consumption.

If the car is now driving normally then this is not necessarily a cause for urgent concern, but you may wish to get the car inspected for this issue. This is something that would not necessarily be picked up during an MoT unless there was a component that was not functioning. If you are concerned that you cannot get the car booked into your local garage in time, you may wish to find an alternative Volkswagen specialist - you can search for one using the Honest John Good Garage Guide here: good-garage-guide.honestjohn.co.uk/