The suspects, aged 37 and 41, both from London, were being interviewed at separate police stations last night, seven months after the killing.
Police have also recovered a car that featured in CCTV footage. Patel, 29, was off-duty when she was attacked outside her house in Wembley.
She was found in her nightclothes and police say she may have come out of the house after hearing someone tampering with cars parked outside.
In September, detectives said they had found the knife used to kill her, a cook's knife, which had been missing from her kitchen since the attack. She was buried in June at a ceremony attended by hundreds of colleagues and 100 officers dressed in full uniform.
