Apparently Burnham wrote a letter to ministers, in which he said this:
I am clear in my conviction that the Brexit deal negotiated by the Conservative government was not good enough for Britain… It has led to a decade of low growth, burdened businesses with more red tape and weakened our ability to control immigration. It is a harder Brexit than was promised at the EU referendum.
…we will need to consider the UK’s long-term relationship with the EU as part of our 10-year plan. I will set out the next steps for this process around the [UK-EU] summit.
Hopefully that summit brings some good news (i.e. closer relations between the UK and EU).
Brexit didn’t actually go through until after the 2019 election. During which Boris Johnson campaigned and made many promises about Brexit, eg it was “oven ready” and absolutely would not be a hard Brexit. They claimed to have had better trade deals ready.
There were plenty of promises made. Boris was even put on trial in 2019 for his 2016 Brexit campaign lies, where he only got off on a technicality because the Brexit campaign wasn’t technically part of his ministerial duties. Everything since the 2019 election was, though, yet he was never charged again - even when he was caught lying to the queen.