Hi. I wanted to let you all know that Viapath laboratory at St Thomas hospital now offers active b12, homocysteine and MMA tests by post. You need someone to take the blood, but the samples don't need to be spun. You post the blood tubes back to the lab. They have to be posted on Mon, Tues or Wed, so that they don't sit in the post over the week end and you have to pay, but they are cheaper than a lot of other private labs. Here's the link
I hope that's helpful to some of you.