Complex sentence: Many contemporary English nationalist movements are associated with support for right-of-centre economic and social policies, but nationalists elsewhere in the UK tend towards a social democratic political stance, as evidenced by the policies of the Scottish National Party and Plaid Cymru.
Split into simpler sentences: Many contemporary English nationalist movements differ significantly from mainstream Scottish, Welsh and Cornish nationalist movements insofar as they are often associated with support for right-of-centre economic and social policies. Nationalists elsewhere in the UK tend towards a social democratic political stance, as evidenced by the policies of the Scottish National Party and Plaid Cymru.