Often (normally?) employers who contribute on behalf of an employee only do so on a matched basis - e.g. they will match employee contributions up to some capped percentage of gross. It's unusual, but presumably not unknown, for employers to (unilaterally and without preconditions regarding matching of contributions) to contribute as you described above. But are you sure that this is what they are doing? If they do this then there should be no catch other than if you leave the job/scheme before two years membership of the pension scheme then you will not be able to retain the benefits of the employer contributions (unless the scheme rules have a shorter vesting period than the statutory minimum of two years).