Migration of Redstart

In the Lincolnshire Wolds this week, we saw a small flock of birds that I didn't recognise and had never seen before.  Similar size to a sparrow, but had quite distinctive russet brown plumage and dark grey/black wings. Found out they were Redstart, but that by now they should have migrated to warmer climes and, also that they are not usually found in this part of the uk. Anyone else seen any ?