Currently, banks must process payments on a T+1 basis even if they suspect wrongdoing, which limits their chances of halting transactions involving fraudsters. Regulators have proposed T+4 for certain cases.
"The Financial Conduct Authority warned last year that come payments groups 'freeze a disproportionate number of accounts for too long and without adequate explanation.'"
https://www.ft.com/content/1911725c-2900-4b28-9c54-b6810479b0af