How is parliament ineffective?

Whereas a government with a large majority can usually rely upon the whips to persuade sufficient MPs to support its agenda, a slim majority, or a coalition, can make this much more difficult.
When University College London examined 12 bills from 2005-2015, they found that 60% of government amendments that made substantive policy change were traceable to parliamentary pressure.
BBs rebelled on 35% of votes 2010-15.
If whips expect significant opposition, they might withdraw a bill e.g. Conservatives dropped tax changes in 2015 on risk of rebellion.
In March 2016, 27 Conservative backbenchers helped defeat the Government’s plans to extend Sunday trading hours.
The Lords made several amendments to the Legal Aid, Sentencing and Punishment of Offenders Act (2012) but these were easily overturned because the Parliament Act (1911) gives the Commons financial privilege.
In February 2017, May’s Government abandoned the Dubs Amendment scheme, after admitting just 200 such children, and pledging to accept only 150 more.
Furthermore, in March 2017, peers made two significant amendments to the European Union (Notification of Withdrawal) Bill (2017)
However, after both amendments were swiftly overturned in the Commons, the Lords accepted the bill in its original form.

Select Committee Chairs are still paid significantly less than even the most junior minister – not attracting and keeping the most talented MPs.
Ministers are often very skilled at avoiding answering questions or giving a different answer to the question set.
Sec of State for International Trade Liz Truss refused to appear the Int Trade Committee in 2019. The Liaison Committee scrutinises the PM twice a year – only meets for 4 hours every 6 months – Johnson failed to attend 3 consecutive times in 2019.
Prime Minister’s Questions is political theatre rather than proper scrutiny.
MP’s will generally try to embarrass the PM by highlighting policy failures – provides parliamentary theatre rather than effective scrutiny. Qs are usually pre-prepared and used for partisan point scoring.
David Cameron’s decision to authorise drone strikes in Syria in September 2015 demonstrated that, despite the developing convention that Parliament should approve acts of war, the PM can still act against the express wishes of Parliament.

Only thirteen Fridays are allocated each year for PMBs, which amounts to a maximum of 65 hours, in which a large number of bills aim to be considered.
The Citizenship (Armed Forces) Act (2014) was one of just three ballot bills to pass that year, while the Assisted Dying Bill (2015) was defeated 330-118, despite polls showing that 82% of the public support such reforms.
They have little chance of success without government backing as exec control legislative timetable and can use ‘guillotine motions’ to limit debate on certain bills, as Cameron did in 2011 on AV System.
It is harder for UK MPs to feel that they have a personal mandate, and they may well feel compelled to follow the party whip even when constituents disagree, because they owe their position in the House of Commons to their party.