How isn’t representative democracy working well in the UK?

Turnout has declined, the Lords remains unelected, and MPs and peers are unrepresentative.
Turnout at the 2015 General Election was just 66.1%, far below the high levels of the 1970s, (turnout reached 78.8% in 1974) – low turnout makes it harder for even a majority government to claim a strong mandate for their manifesto policies.
Some argue that the House of Lords is noticeably undemocratic and out-dated for a modern representative democracy – both chambers are also criticised for being descriptively unrepresentative.
While a record 191 women were elected in the 2015 General Election, making up 29% of the House of Commons. In March 2017, there were 207 female Peers in the House of Lords. Only around 6% of MPs and peers are from ethnic minority backgrounds, compared with around 13% of the UK population.

The fusion of powers and party system can give governments significant control over Parliament.
Any government that enjoys a sizable majority in the House of Commons can be very difficult to defeat.
At the 2015 General Election, the Conservative Party won 330 seats (50.8%) with just 36.9% of the vote. As turnout was just 66.1%, it is arguable that there are insufficient checks on policies that only 24.4% of eligible voters have actually endorsed.
Some voters may feel that, once in power, they have too little influence over the governing party – Before becoming Prime Minister, Theresa May was, like a majority of her constituents in Maidenhead, firmly against plans for a third runway at Heathrow. However, since becoming Prime Minister, she has endorsed the plans, arguing that the expansion is in the wider national interest.