Is my employer entitled to reclaim my bonus from my final paycheck following my resignation?

I am leaving my employer of the 3rd June, following hading in my resignation on the 30th April. 

On the 24th April I recieved a bonus for my efforts in the 2017 calander year. 

My employer is now reclaiming this bonus as I am leaving with 3 months of recieving my bonus. This is stated in their discretionary bonus scheme T's and C's. However they can change those at any time and solely at their own discretion. 

For further context I am on an open ended contract which could be termintaed with a months notice by either side. 

My question is would this payment reclaim stand up in a court of law?