Getting a gas hose to fit the oven isn't a problem as they will all fit to the oven its the connection to the gas supply in your home.
If you have a normal gas pipe fitting bayonet tap then you need this hose click here
The BS699 is the hose that meets the british standereds so as long as the ends fit that will be fine.
What it means is the gas pipe copper end are made to British standerd its like a safety standerd which they have for rubber gas pipes. just like anything else.
So all the gas pipes will be BS669 otherwise they cannot sell them.
Ok you had edited the question once I replyed that's why I didn't see the full question sorry.
You just need the black rubber hose if its just an oven.