Course change first term of uni!

Let's say I have already applied for mechanical engineering at different unis but once I get to university, I've been thinking I might want to switch from mechanical engineering to like "maths and economics"

Given that the unis in contention are :
ucl,
imperial,
bath,
bristol,
warwick.

What unis you reckon will allow me to switch from mech eng to maths and econ in my first term ( given that my alevels are maths, further maths and physics )

Let's say I have already applied for mechanical engineering at different unis but once I get to university, I've been thinking I might want to switch from mechanical engineering to like "maths and economics"

Given that the unis in contention are :
ucl,
imperial,
bath,
bristol,
warwick.

What unis you reckon will allow me to switch from mech eng to maths and econ in my first term ( given that my alevels are maths, further maths and physics )

in general - the earlier you ask the more likely that a switch will be possible. If you ask NOW then they're more likely to be able to help you than if you wait until after you've enrolled on the wrong course.
There's no guarantees that a switch will be allowed so it's generally a bad idea to enrol onto a course hoping to switch. Universities are wary of any applicants/students attempting to "switch" after enrolling in order to avoid meeting entry requirements for over-subscribed courses.
It looks like Imperial might require you to have taken the TMUA

Yeah of course, but for me gap year is just not an option. To be fair, I'm more worried about the more competitive universities, such as imperial and ucl and warwick and if they would let me. Luckily, I did the TMUA anyway ( only got a decent **** score ) but it will do as it was slightly above average score of applicants this year. But surely if I ask them for help now they will just tell me its not looking possible?