Have just ordered full fibre, when they come to install outside box will I have a choice where they put it
With in reason. Speak to the installer and if they can accommodate where you want it they will put it there or explain why not.
Is the current service delivered overhead or underground , if it’s an underground duct and the duct appears on an external wall , then the chances are the CSP will be sited pretty much where the duct appears, if overhead , (or underground but not a ducted feed to the external wall ) , you may have some choice where the CSP is mounted, although with overhead they will ( if possible ) use the existing fitting on your house where the copper dropwire attaches.
The installer will try and provide the CSP , within reason , where you would prefer it to be fitted, as long as your request isn’t unreasonable or impossible you should be OK.
Does you question just concer the outside CSP or where your internal ONT is installed?
Normally the outside CSP is installed it just above the exit from the duct from the property or directly (changeable) below an overhead one.The engineer will the run an exterior cable to your required to the ONT you request if possible.
Note: If you get a contractor install they will do it as fast as they can as they get paid per job. The quicker they do it the more they get paid.
Its under ground and the connection is between our bungalow and next doors so they will probably come down to end of bungalow. But I would like them to come in about six foot from end where i will have necessary sockets to plug in router.
The CSP will be installed directly above where your current telephone line comes out of the ground. I can't imagine a problem with the entry into the property being a few feet from the CSP.