Do both partners have to take SPL/ Can just the Mother take SPL?

SPL can be taken in three ways; both parents take leave, just the Mother takes SPL or just the father takes SPL (Mum remains on maternity leave). To clarify, the father does not have to take a single day of SPL in order for the mother to. The easiest way to convince an employer who doesn't believe this is to show them the governments own advice on applying. 

If you click on the link to the forms on this page and then download them the first thing you see is this table which clearly shows the three ways in which leave can be taken. 

If I 'return to work' for the holidays does my partner then have to take the time off?

This question is somewhat answered by the one above, in that SPL can just be taken by the mother. But to further clarify, both parents have a legal entitlement to take three blocks of SPL. These blocks can be taken at anytime (for the mother after curtailing mat leave, for the father anytime after the mother has given notice to curtail, so a father can take SPL whilst the mother remains on mat leave.) . The only qualification is that between you you cannot take more than 52 weeks of maternity and shared parental leave combined (the 2 weeks paternity leave does not apply here).