Depending on the sums involved, it might be worth taking proper advice on your tax position.
The details are too sketchy to advise properly. If you were outright gifted shares at the time then I would have expected you to have suffered tax at the point of the gift (3years ago)
They were gifted 3 years ago under the provision that I had to be employed by the company for a further 3 years no monetary offer was given at the time. When I left, it was part of a re-structure of my role and as such the company agreed to honour the shares and my share save scheme. It's a little mess, the shares themselve it's not a huge amount but on my bag of a beer mat calculations it was enough to get a new kitchen fitted and get some flights booked for Vegas (cheap seats) but I'll now be putting the holiday on the back burner.