The international development secretary was ordered by the PM to cut short an African trip to fly back to the UK.
BBC political editor Laura Kuenssberg said a source told her that Ms Patel would rather resign than be sacked.
Ms Patel apologised on Monday to the PM about unauthorised meetings with Israeli politicians in August.
But there are now questions about further meetings held in September.
Ms Patel's flight from Uganda landed at London Heathrow 15:10 GMT. She arrived via the back door of Number 10 at about 18:25 GMT for her meeting with the prime minister.
The BBC's diplomatic correspondent James Landale said that by holding the secret meetings with Israeli officials, Ms Patel had broken "one of the cardinal principles of government, namely collective responsibility, the idea that government speaks and acts as one once a policy has been agreed".
He said this was about practicalities - so part of Whitehall knows what the other part is doing - and it also ensures ministers remain accountable.