Use to have a full-time, fixed term contract, ending this November. Applied to go part-time (3 days per week) recently as my wife and I had our first child a few months ago. The idea being that the pot of cash used to pay me would extend my contract for a extra few months. After a friendly meeting, it was agreed that I would start part-time on 1st June and would hear about my new end date shortly, once it was calculated.
Got a signed letter this morning extending my contract by 2 years. I've told them, but both they and I have signed the new agreement with this newdate... what can/will they do?
Ps. Employer is a broke science department at a big university. Pot of cash is a (small) research grant.

