Remember that even if they don't hit zero, if they're underwater, say, £1299.99 they are worth essentially zero as you'll not want to exercise them (and why would you want to? You'd be losing money - and you can't write it off as a tax loss in almost all circumstances).

Then, unless they're publicly traded, or there is a legitimate secondary market, you can't even do a sell to cover.

The other way of providing equity is with RSU's, restricted stock units, where the company promises to give you, at each vesting date, a portion of stock. The problem there is that this is taxed as income on the value of the stock at vesting, and once again if there is no secondary market you'll not be able to sell enough to cover your tax liability and be in for a nasty invoice from the IRS that you need to scramble to cover.

I'd recommend having a financial planner walk through the ins and outs with you.