Your author does not like the draconian restrictions of pre-booked cheapo "Advance" tickets, but when carefully managed, they do save cash. fbb's ticket to Leicester was on a Nottingham bound train and these are usually HSTs. But travelling from the Island, the bit of the journey on SouthWest Trains has no time or seat-booking restriction, so fbb could leave earlier (even during morning peak), travel cheaply (£13.50 single with OAP railcard, Portsmouth to Leicester including the cross-London Undergound) and still have time for a relaxing lunch at St Pancras.
But there remains one tricky part of the journey. His overnight stop was c/o long-time chum David who lives at Groby, an ancient village (now suburban dormitory) some 5 miles north-west of King Richard III's extended resting place. And the bus leaves from St Margarets Bus Station.