ok we bought one of thesehttp://www.jmldirect.com/Pest-Shield-PP1020/
worked great for 3 days and the rats came back.
I have finally managed to get the council to put a camera down the drains to see if there was a hole or crack. they did this today and thankfully all the pipes are fine just badly laid and held together, also found fresh rat droppings so they baited again.
so after the enforcement officer looked at my building plans for the houses she has now said as my garden and drive have sunk the rats have found a void under them and this is how they are getting in the walls as the house wasn't built to spec and my cavity walls at the front of my house are not deep enough in the ground or not correctly built in some way .
Her advice for a solution to this problem is to dig up my entire driveway pack it properly and build it up again to ground level,then relay the drive correctly, she also said i need to dig away at my little front garden, find where the rats are getting in and block it then pack it properly and then lay patio slabs.
so on top of suing the flaming builder we now have to sort this mess out.
But i would like to thank everyone for the advice given when i requested it a few weeks ago