Harry, the simple answer is that I don't know, as our lot seem to be the Irish branch.
My gt gt g-father was William Leece who died in Liverpool in 1860. The 1841 and 1851 censuses have him born in Ireland in 1790-something, the exact year a little uncertain depending on which mid-19th century record you use as a starting point.
The only other Irish Leece link seems to be the Manx-born sisters Anne and Sophia Leece who died in Dublin in 1818 and 1819 and are buried in Rathfarnham Cemetery.
A very tentative hypothesis might be that William, Anne and Sophia were brother and sisters, three of the four orphaned Leece children provided for in the will of William Leece 1725-1804, Manx-born merchant of Liverpool. But the evidence is hardly conclusive, and there are other details in the family tree that perhaps point away from this. All rather puzzling.