My employer recently had another round of meetings, trying to encourage people not to opt-out and extolling the benefits. At the moment, to put 1000 GBP into a pension pot will lower an employee's take-home here about 350 GBP - the company is doubling it (up to 5% of the salary), the government is giving the tax back, and the company is doing it by salary sacrifice so your take-home isn't so badly affected (tax etc. goes down a bit, offsetting a little the money the employee puts into the pension). They can choose what to put it in; stocks, funds, cash, treasuries. They can move it between providers, it's theirs. The only restriction is they can't have it back until they're at retirement age (not even retired; just at the right age, I think).
Even so, many people say they'll not bother, thanks. Some say they rather just save the money up themselves (costing them an incredible 1000 GBP for every 1000 GBP they save - three times the cost!). I know that putting it into a pension has risks and downsides, but given that the pension is basically tripling their money on day one, it seems incredible how many people aren't interested. Makes me fear that if people aren't interested even with (what seems to me) such a good deal, what are people without such sweeteners doing.