ADT Tad

I worked for a US based company in Singapore and was provided with stock options that were an allocation of around 5 to 10% of my monthly salary so I did not pay for them but they were simply allocated to me. I have now left Singapore and settled my tax affairs for the stock options whilst in Singapore and did not Expedia’s or sell any, but I was still liable to pay any taxes due on the stocks whilst in Singapore. I’m now back in the UK and classed as a UK tax resident and work for a UK organisation. if I was to exercise or sell my stock options, what would be my tax obligations in the UK?