Yes, at a moment of inflation, they announce significant tax cuts which will have a big inflationary impact. The Bank of England was already behind on interest rate rises, and now the government is relying on them to not only counter global trends (high rates in the US causing devaluations basically everywhere), and also the inflationary effect of energy cost increases, but also extra inflationary tax cuts. That will force rates high (apparently the market is pricing in an increase to 5%), which will then cause big reductions in housing, and negative equity.

The thing I am confused about is why this happened at the announcement. The big measures had already been announced, an energy price cap (£60bn or more depending on wholesale gas costs), and reversal of planned tax increases in National Insurance and Corporation tax (about £40bn). The additional unannounced tax cuts were small (for instance the cut in top rate tax was £2bn). So it seems that most of the drop should have happened before.

Apparently the PM wanted the announcement to feel radical to distance her from the previous government, so maybe the markets were responding to the feeling of the announcement, and the implication of future radical ideological action, as much as the numbers.