Powers of House of Commons and the House of Lords

The House of Commons has, theoretically, a massive amount of formal power.
It has a sovereign legislature, and can make, amend or un-make any law it wishes, and can be only delayed by the House of Lords. Can remove the government of the day in a vote of confidence. E.g. 1979 vote of no confidence in James Callaghan's Labour government.
However, in reality it has only a limited influence over legislation due to executive domination of the House of Commons: the Westminster voting system offers the government majority control over the Commons and the party discipline system allows ministers to control backbenchers.
Formal mechanisms to ensure accountability like Question Time and select committees are often relatively weak.
But, declining levels of party unity have led to more independent, educated and assertive backbenchers, who are able to exert a greater influence. E.g. Conservative backbench rebellion 2011 on having an EU membership referendum, where a massive 81 conservative MPs voted for having it.
However, counterbalancing this is a growing trend for landslide majorites, which allows governments to resist pressure from backbenchers and opposition.

The formal powers of the House of Lords are, in contrast, quite unimpressive.
Lords can only delay legislation from the Commons for a year maximum. Cannot delay money-related bills.
Cannot remove the government of the day and can only veto a very limited range of matters like the sacking of senior judges and delay of Westminster elections.

BUT, in practice, the House of Lords often has a greater influence over the government than the Commons. E.g. Tony Blair's government was never defeated in the Commons but had 353 defeats in the Lords.
Much weaker party system in the Lords than the Commons. Since peers aren't elected, they cannot be made to 'toe the