What is wrong with my Fiesta??

I bought my R reg Fiesta 1.25 in 2006 and I had no real problems with it until last summer. I usually drove it at least every other day, and for long distances about once a month, and then all of a sudden it wouldn't start at all after being left alone for just 4 days. A kindly RAC man charged the battery for me and then it seemed to be back to normal. I had it serviced in November and the MOT is due in a couple of weeks.

For the last couple of weeks it has been sluggish to start for some reason, then today it was very hard to start but eventually kicked it. The engine tries to turn over and does eventually, but it's worrying. Always have to depress the clutch and pump the accelerator before I turn the ignition, which I never used to and surely shouldn't have to for a car this age. Then today I got into my car after work to a very strong petrol smell inside the car, not outside at all, just inside. My dad tells me the carburettor is probably at fault.

Also, from May last year I have noticed quite a loud 'knock' noise when I apply the brakes, happens at least 50% of the time. I took it to Kwik Fit for a free brakes check and it's had a service since then, and no one has mentioned it or offered a solution!

Any thoughts would be appreciated! Cheers.