The Parliamentary system means that there is no separation of powers, so "total control of power" just means a parliamentary majority, and most governments have been one-party majority governments (there have been a few coalition governments, such as the LibDem-Tory coalition that Cameron started with, but they are the exception, not the rule.)

Now, if the UK had proportional representation, even with a parliamentary system, that might make one party acheiving total control more difficult than in the US, and enough parliamentary systems are also PR that people sometimes conflate the effects of the two features.