David Cameron, the former Prime Minister of the United Kingdom, made several significant mistakes and miscalculations during his time in office (2010-2016) that had lasting impacts on British politics. Here are some of the most notable:

    The 2015 EU Referendum: Cameron's decision to hold an in-out referendum on EU membership in 2016 was intended to settle divisions within the Conservative Party and appease Eurosceptics. However, he underestimated the strength of the Leave campaign and the discontent among voters regarding the EU, which ultimately led to the Brexit vote and significant political turmoil.
    Handling of the Scottish Independence Referendum: While the 2014 referendum ultimately resulted in a vote to remain in the UK, Cameron's approach to the campaign was criticized. Many believed he did not sufficiently engage with Scottish issues or the concerns of the Scottish electorate, which fueled nationalist sentiment and led to increased calls for independence.
    Austerity Measures: Cameron's government implemented severe austerity measures following the 2008 financial crisis. While aimed at reducing the national deficit, these policies led to widespread public discontent, protests, and criticism regarding their impact on public services and social welfare. The long-term economic effects and social consequences of these measures have been debated extensively.
    Failure to Control Party Factions: Cameron struggled to manage the divisions within the Conservative Party, particularly between moderates and hardline Eurosceptics. This division became increasingly pronounced leading up to the Brexit referendum and contributed to his eventual resignation.
    The "Big Society" Initiative: Cameron's vision of the "Big Society," which aimed to empower communities and reduce the role of the state, was seen by many as vague and poorly executed. It failed to gain traction and was criticized for lacking a clear strategy or sufficient funding.
    Response to the Syrian Civil War and Refugee Crisis: Cameron faced criticism for his handling of the Syrian conflict, particularly regarding military interventions and the UK's response to the refugee crisis. His decision to intervene in Libya in 2011 also faced backlash due to the subsequent instability in the region.
    Overconfidence in Polling: Leading up to the 2015 general election, Cameron and his advisors were overly confident in their polling data, believing they could secure a majority. While they did win a majority, the confidence in polling led to complacency in campaign strategy and engagement with key voter groups.

These miscalculations and mistakes contributed to significant political challenges during and after Cameron's tenure, particularly with the rise of Brexit and the subsequent leadership changes within the Conservative Party.