PM can use prerogative power to dissolve Parliament
Senate is elected, Lords isn't
Staggered Senate terms, whole Commons elected at once
Elections to devolved bodies use PR
2-term presidential limit, no limit for PMs
President is de facto party leader, PM has to be party leader
UK party leaders nominated by MPs (sometimes members), presidential candidates chosen through primaries/caucuses
Constituency boundaries drawn by an independent commission, congressional districts drawn by state legislature
UK has much stricter campaign financing laws