I think these compulsory pensions at the moment are pretty much a waste of time where the employer chooses the lowest rate 2% I think, aprticularly (as with my employer) the employer tries to find a way of passing on its obligation to paya matching amount. I worked somewhere recently for four months and accrued a pension pot of £80. I couldn't get an annuity with it and to cash it means I've got to get a copy of passport signed by a doctor/solicitor plus poof of address and bank account just to prove my identity. Okay, if I'd worked there for 40 years it would have been worthwhile and maybe it will be better when the minimum increases to something like 6%.
I know some employers who use zero hours type contracts will try to ensure their employees' hours and pay falls just below the threshold so some will miss out