Thanks for the support guys, it is a weird reaction that you can have to these things. You don't want to over-react but you do want to take precautions - just incase.
Well... just as I finished typing the post another gas man (in a bigger flouresent jacket, so he must have been more senior

) came to the door to tell me to switch off the electricity. He said that they HAD been told by the police that they should evacuate the area, but, it was pretty far away, so its probablly OK to stay

It might all be over in an hour, they would let me know if I had to leave.
So I switched off the electricity and packed a bag with my i-pod and phone (neither of which were charged, so I don't know what I was planning with them

) in case I had to be moved somewhere for the rest of the day
I sat knitting in the dark with the curtains closed, waiting for the all clear -quite pleasant, but it would have been nice to listen to radio 4

(wind-up radio is going on the shopping list)
Anyway I peeped out of my curtain (for fear that my head would be ripped off by a massive gas explosion) and everyone was gone, no police, no gas type people apart from one of the flouresent jacket brigade who was returning to her car, smoking - So I guessed it was all sorted - Thanks very much for letting me know guys
The last time I had an odd knock at the door it was immigration trying to deport me and asking to see my passport

(I don't travel so I don't have one) and I had to answer questions about where I was born, where I had lived, where my husband was born, etc.
I have to admit that the immigration story is much more exciting (especially because I was 2 months pregnant at the time and thought that I was going to be carted off somewhere to be questioned.