Sorted it drastically though but the story so far.
In total here's what I've replaced (some parts were changed even though I knew they wouldn't cause the suction fault but they were on the way out anyway).
new rear hose and wand handle as old hose was duct taped up years age and wouldn't come out of the handle!,
new bin flap as clip had broke on one side,
new drive belt as old one had expanded and was allowing the base assembly to drop down, slightly on its side pivots and in turn allow the belt guard to catch and not return into position.
New brush roller as old one was badly scored and had miles of cotton and carpet threads around it that I couldn't be arsed to clean it!
Finally the soleplate.
After all this my wife still couldn't cope with it so I did what I tried at first and raised the new soleplate up by sticking strips of cushion flooring onto the soleplate, this works as it slightly breaks the seal between the carpet/kitchen floor but still sucks up dirt.The drawback is that they would eventually fall off.
So I bit the bullet and experimented with drilling holes in the rear vertical wall of the old soleplate (as seen on YouTube) then after finding what size worked best put one 8mm dia hole into the new one - voila!
My wife can now push it around and it vacuums ok.
One thing worth mentioning is that I contacted Dyson at first and though all they seemed to want do was sell me a service call, they did say that the suction can increase if the motor is getting close to replacement.Two Manchester repair shops said they had not heard of this before hence I went down the soleplate route but I have noticed marks on the old belt like melting and the motor shaft is extremely hot after using the vac for a few minutes is this heat normal?