A British Muslim convert was jailed for at least 14 years on Friday for plotting to blow up London's St Paul's Cathedral and then herself in a suicide attack on the London subway.

Safiyya Shaikh, 37, confessed to plotting the attacks when she was arrested after making contact with an explosives expert who was a police informant.

The heroin user, who converted to Islam in 2007, expressed no remorse as she was sentenced at London's Old Bailey, gesturing to reporters using the Islamic State one-finger salute as she was led away.

Prosecutors also disclosed details of a call she made to a friend from prison in which she said: "I didn't get cold feet, yeah - I was ready to go through with it."

The court was told she intended to trigger a suicide vest at the nearby London underground station immediately after detonating the cathedral bombs.

Judge Nigel Sweeney sentenced Shaikh to life in prison with a minimum term of 14 years.

He said her defence team's claim that she had changed her mind about going through with the attack prior to her arrest "was a lie".

"Your intention had been - and remained throughout - strong," the judge said.

The investigation showed that she had confessed in August last year to undercover agents that she "would like to kill a lot".

She visited St Paul's Cathedral - a popular tourist destination facing the London Stock Exchange - in September on a reconnaissance mission and was arrested the following month.

London's counter-terrorism police chief Richard Smith said Shaikh "loved watching graphic videos of terror" and changed her name from Michelle Ramsden after a "truly traumatic childhood".

Britain has witnessed three terror-related attacks in the past year.

A convicted jihadist who was out on parole after serving a sentence for terror offences was shot dead by police after stabbing five people - two fatally - by London Bridge in the heart of the British capital in November.

Armed police killed another assailant who injured three people in a stabbing attack in the Streatham area of south London in February.

The most recent attack saw three die in a stabbing rampage in a park in Reading, west of London, last month.