Can't find water stop tap

We have searched everywhere and we can't find the indoor stop tap only the shared one on the drive. Is it possible to have one fitted if there isn't much room under the sink to put it? My dad doesn't think theres room and we'll need one at some point to sort the downstairs toilet

Depends where your mains inlet for the water is - not necessarily under the sink. If you can locate that there should be a tap somewhere. If there isn't yes you can fit one, you just have to turn the water off using the tap under the little man hole cover (usually one per house but not always - little metal cover about 2cm sqaure in the ground) outside your house somewhere

Just get a plumber i am sure he will sort it no prob