Tehran rejects "accusations" put forward by a British security official, Iran's foreign ministry spokesperson Esmaeil Baghaei said on Wednesday, a day after UK's MI5 spy chief said 20 Iran-backed potentially lethal plots had been disrupted in Britain since January 2022.

In a wide-ranging speech on Tuesday outlining the current threat picture, Security Service (MI5) Director General Ken McCallum accused Iran of being behind "plot after plot" on British soil.

McCallum said state threat investigations were up 48% in the last year as Russia and Iran turned to criminals, drug traffickers and proxies to carry out their "dirty work".

Iran's foreign ministry spokesperson dismissed what he described in a statement as repetitive accusations over the last two years by the British security official, whom he did not name.

Baghaei accused the British of hosting "terrorist" groups that take advantage of free speech to promote violence, according to the statement and asked London to reconsider its policies towards "the nation of Iran and West Asia".