Hi Chris,
I really feel for you. The same happened to me a while ago and your heart just drops and panic sets in!!!!
Since then I have done the following..
1. Really take your time when cutting through floorboards. Try and take floorboards up that have already been up, therefore no sawing required. If you are going to saw then work out the depth of the floorboards and cut ever so slightly less and just snap the last bit. maybe even take other floorboards up that require no sawing, put a camera down and look over to where you are going to be cutting.
2. look at where radiators are, is their likely to be pipes where you are about to cut.
3. Don't rely on a pipe/cable finder, there are no reliable ones, they just confuse you with their false readings.
4. Get these..
https://www.amazon.co.uk/Rothenberger-Kibosh-Emergency-Repair-Plastic/dp/B00JOCTVL4.
There is a 15mm one and a 22mm one for the popular pipe sizes. However, they are only useful if you can actually get the clamp around the pipe, i.e a single pipe by itself with no others right next to it.
5. Go on a DIY plumbing course or at least go on the net and learn how to make an emergency repair to a pipe.
6. If you do go through a pipe, either in the wall or floorboards just get to the pipe as quickly as possible. Dont worry about making a mess of the wall or floorboards as that is nothing compared to the damage the water will be doing!
7. Have a plumbers number in your phone.
8. If you cannot do any of the above, just run away........ quickly!