Complex sentence: Billericay (now in the seat) was not a bellwether: since 2001 it had a Conservative MP, John Baron, on the abolition of the seat and secured re-election in the new seat at the 2010 election.
Split into simpler sentences: Billericay (now in the seat) was not a bellwether--since 2001 it had a Conservative MP. Baron on the abolition of the seat secured re-election in the new seat at the 2010 election.