One of my friend has an expired passport of Pakistan and living in UK. How will he be travelling back to Pakistan? Any letter he needs as renewing passport will take long time and he wants to travel soon. Any suggestion please.
Your friend's only course of action is to apply for a new passport (or perhaps another emergency travel document) at the High Commission or a consulate of Pakistan. If it takes too long for your friend's travel plans, there is not much to be done.
Renewal shouldn't take that long. According to the website of the High Commission, regular applications are processed in 20 days, and urgent applications, the surcharge for which is just £20 unless the passport was lost or stolen, take 10 days: http://www.phclondon.org/mrp/fees/