Very low calorie allowance?

Set your goals so your number shows 1800 and don't eat back excersize calroies. This should be your TDEE-20% method. MFP uses a method that will require you to eat back your excersize calories and a lot of people find that method unrealiable. I, like everyone else here, inputted my numbers and MFP gave me 1200 calories. I did that for a couple months and practically starved myself. Then I heard of the TDEE method and calulated it. I adjusted my numbers in MFP to put me around 1800 and I'm steadily losing at a pound a week. That's healthy for me because I'm no longer in the obese range. Yay!!! We all want to go for a 2 lb a week loss but's it's not always sustainable or possible. I found I could loose just as much, if not more, by eating more and fueling my body rather than starving it. If 1800 is what you did on WW and it worked for you, adjust MFP to reflect the same. If it ain't broke, don't fix it.

You clearly screwed up your goals. Go to My Home > Goals > Change Goals > Guided and make sure everything in there is accurate. Make sure you don't have it set to 2 lb/week as well. If you're maintaining, set it to maintain your current weight. Then see what happens. If it's still low, which I doubt, manually change your goals by following the instructions above, but selecting "Custom" instead of "Guided."

Blimey 1200 calories for a 16 stone bloke??? If you were losing 2.5lbs on 1800 cals then definitely don't go lower. As you get closer to your goal I'd advise upping your calories and losing a bit slower but for now if I was you, I would be aiming at least 1800.

You clearly screwed up your goals. Go to My Home > Goals > Change Goals > Guided and make sure everything in there is accurate. Make sure you don't have it set to 2 lb/week as well. If you're maintaining, set it to maintain your current weight. Then see what happens. If it's still low, which I doubt, manually change your goals by following the instructions above, but selecting "Custom" instead of "Guided."

Change your GENDER too. MFP defaults to 1200 for women......men need more calories....something is not right.

MFP uses the data you give......If you put down "I want to lose 2 pounds a week" ....when 1 pound is more appropriate....it just defaults to the lowest value. Also, MFP doesn't give you exercise "credit" until you log it. You may "earn" extra calories.

To be fair, a lot of people get a low calorie goal on MFP because they choose the wrong information and not account for exercise. You will get people comparing their MFP goal at 2lbs a week weight loss goal to TDEE -20% (which is about 1 lb a week). If you are doing it correctly, both numbers should be close when exercise is accounted for.

TDEE -20% and MFP plus exercise always ended up with me having the same average calorie intake over the week.

I agree with you. TDEE - 20% (which was 1lb for me) was about the same amount of calories that MFP suggested when I picked the right activity level, weight loss goal and added my exercise in. A lot of people want to lose weight unrealistically fast and automatically set a weight loss goal of 2lbs.

Change your GENDER too. MFP defaults to 1200 for women......men need more calories....something is not right.

MFP uses the data you give......If you put down "I want to lose 2 pounds a week" ....when 1 pound is more appropriate....it just defaults to the lowest value. Also, MFP doesn't give you exercise "credit" until you log it. You may "earn" extra calories.

MFP doesn't "default to 1200 for women." Many women indicate that they want to lose two pounds a week, which would require a deficit of 1000 calories a day. Especially when one is only, say, 10-20 pounds above "normal" BMI and chooses the "sedentary" activity level in MFP, this choice will result in a daily target that is below MFP's minimum of 1200.

No argument with the parts about exercise and gender above. Just don't want to see the "I'm female, so this is what MFP gives me" trope propagating further. It's a case of the user being more aggressive than many MFP veterans would advise.

Thanks for the advice everyone. Eating back calories burned seems counter-intuitive to me but I've heard many people advocate it. I've also been speaking to people about how to correctly measure calories burned and no-one seems to have a definitive answer and I know from my own experience that estimates vary from method to method sometimes wildly so. So its fine suggesting you eat back your calories burned, but while theres no reliable way of calculating this hows it possible to be anywhere near accurate?

Eating back exercise is not really counterintuitive if you understand how this site works. You are already at a deficit. When you exercise you create a larger deficit. For a number of reasons, people recommend keeping a moderate deficit.
In other methods, like TDEE, you also "eat back" the exercise calories, but they are already accounted for in the original formula.

Things like walking and running are fairly well established. The problem comes in to play where you have one type of activity that can have widely varying intensities, like workout videos, weight lifting, etc.
Lots of people have had success using MFP's entries. Personally, I under log time. And if I am burning more than 600 calories and hour (which is what I would if I ran that long) I'm going to question that estimate. It's worked for me.
You don't need to be exact. You just need to be consistent. Some people only eat 75% back. If after several weeks you aren't seeing progress (like more than 2 or 3 weeks) you can adjust downward. That is assuming your food logging is accurate as well.

Or you can go the TDEE route. It also accounts for activity but gives you a set goal every day.

You are going to get people who tell you to get a HRM. They are useful but can be inaccurate as well. You don't "need" one. Also keep in mind they are designed to estimate calories during steady state cardio activity and outside of that will become less accurate.