Flying BSL-FRA-LHR (23:20hrs) LHR-FRA (5 days) FRA-BSL. I don't need my suitcase in London.

I am flying to LHR arriving 16.05 on a Saturday and depart 15.35 on Sunday. LHR is only a stop on the way to my final destination (FRA).

(1) When I arrive can I immediately drop off my luggage for the next day or do they not allow this in LHR?

(2) Will I even be allowed to check my luggage from BSL to FRA despite of the long layover in LHR? Will it cause an IT issue because the suitcase would pass twice through FRA?

I guess (2) would be perfect but I could live with (1). Just don't want to take my bag to the city.

Thanks!