Help!!?

Hi, Would anyone be able to advise on the following??

Since yesterday my T reg Ka has been over revving like mad at the end of a journey. I've been braking and as soon as i press down on my clutch it starts over revving like mad. i do need to replace the expansion tank as it has a small leak in it which i found tonight.

are these separate problems? could the leaky expansion tank be causing the over revving or are they completely separate?

Please help!!