Yhyjyk

Does Parliament hold absolute power in the UK?

What I mean by absolute power is: presumably they can make illegal or legal whatever they want. Even going so far as to disenfranchise their own electorate.

Is this correct, or are there any checks on the power of Parliament?

The Fixed-term Parliaments Act means they have to respond to the electorate, eventually. In fact this provision has existed for a long time in various forms

The Septennial Act 1715 provided that a parliament expired seven years after it had been summoned; this period was reduced to five years by the Parliament Act 1911.

The House of Lords can exercise some restraint in terms constitutionality of laws, although given the lack of a single, written constitution in the UK that's a complicated exercise.

Presumably the Queen can withhold Royal Assent on some completely insane law, but there isn't much in the way recent precedent.

The last bill that was refused assent by the sovereign (on the advice of ministers) was the Scottish Militia Bill during Queen Anne's reign in 1708.

Another elephant in the room here is the European Convention on Human Rights, an international convention to which the UK is a party state. This effectively gives a supranational body, the European Court of Human Rights the power to pass judgement that a contracting state has breached provisions in the convention concerning human civil and political rights.

The original treaty does let states leave (denounce the treaty), but only after a 5 year cooling off period. As with all international treaties, it's not entirely clear what would happen if a state just unilaterally stopped playing ball immediately, especially if it were willing to enter a period of North Korean style isolationism, but it is another element in play, beyond the various parties (and the two houses) of Parliament watching each other.