WiFi problem - Speed comparison - 10.10.4 no fix

After updating to Yosemite, my internet speed over WiFi completely tanked. I have a 100Mbps + connection and my laptop was getting approx. 25-30Mbps over WiFi before the upgrade. The laptop nor any other hardware has not moved. Now I get a paltry 3Mbps. I had hoped the 10.10.4 update would have helped but, alas, no.

You can see a comparison of my speeds over WiFi and cable below. Also the info from WiFi diagnostics but I haven't a clue what most of it means. For the record I am about 4m from the router with two partition walls in between and minimal interference. Moving the laptop to within about 1 or 2m of the router with no walls in between brings the speed back up to approx 50/70Mbps which is what I would expect.

It seems to me that whatever has happened in the update to Yosemite has had a detrimental effect on the WiFi receivers ability to capture a strong signal. I have tried different channels, dumping the network preferences and all the other recommendations on the other forums, so I'm posting here in the hope that someone has a similar issue and has found a resolution. My only current solution is to run a cable from the router through my house to the office but my wife won't be long getting fed up with that!

Either way I think it is shockingly poor form from Apple.

Any help from the community would be appreciated.

D