Originally Posted by
Swanhunter
With 5 hours your best option is to clear immigration and customs at T3 and make a free landslide transfer to T5 using the Heathrow Express. This will give several opportunities to knock some additional minutes off your life expectancy.
I agree. ^
This'll get you land side much quicker to enable you to enjoy a much needed smoke. Avoiding the airside bus transfer will also add minutes on to your life expectancy.