Bro i did this back in 2006 when i left the army. Except it was London to Rawalpindi by any means.
If you want to speed through Iran consider the train because it's very cheap but service is good.
I took the route from London by a different path. i got a boat to Norway across the north sea. Then hired a cab to get me from Ognihvia to the Russian border.
I then had to come through the Russain territories skirting Moscow etc.
There is a Steppes highway across the Urals to central Asia. It's good country for cycling or motorbikes until you hit Kazakstan where roads are very bad. You can then make your way to Pakistan either through the Northwestern passages through Uzbekistsan and Afghanistan, this is too risky but short journey. Or you can hit the long road through Chinese territory to the KKH.
When you going to be coming.
I live in London so i could meet you here?
I wish you best of luck.
If you have a British passport then it's best to use that instead of your pakistani one becuase it carries more political wieght (sadly). Best thing to do is to speak to represantatives from the embassies of the countries you plan to move through. E-mail or phone is best, letters they dont bother with, and they make you stand about for ages if you want to speak to them in person. Most Muslim countries respect pakistani citizens especially Turks but Europeans are more resentfull of us (again a sad fact i have experienced) so be wary while you have fun.
If you have to travel through Iran be aware also of the desert and while this sounds funny keep plenty of water and carry a scarf or turban. If your desperate you can filter water through sand wrapped up in your scarf. (I've had to do it so i hope you don't have to!)
If you can think of us in your prayers brother and if you can stop at any Shrine or sacred site on the way make sure you ask the Wali/Syed Sahib e-Mazaar for help. Trust me they can be of greater help than anyone on this site. If you believe, i hope you do?
Finally and perhaps most importantly, be aware of your suroundings try to avoiding being isoloated on your own ( i know you can look afteryourself, but brother i wouldn't risk it if you know what i mean?) Also keep an open mind and observe things as you travel and respect others.
Oh and did i mention brother?
Have fun whatever you do becuase it's the most important part of any trip!
I hope my advise has helped you.
Take care and may Allah guide you and bring you back safe.
If you have any more specific questions feel free to drop me a PM i'll help you any way i can.
Wassalaam have fun Brother and may you forever find happiness wherever you go.
Enjoy yourself!