Westminster system is not a particularly good example of checks and balances, though, given that whole parliamentary supremacy thing. A Westminster-style Parliament is essentially unanswerable to anyone but the voters; and even then it can unilaterally change election laws, so it can circumvent the voters as well. If the courts deem some act of Parliament unlawful, the latter can just pass another act explicitly declaring it lawful (the recent Safety of Rwanda Bill was a good example of just such an attempt).