I wish to renew my portuguese passport/ID in London,UK bwhat should I do?

Don't you have any friends/family in Portugal?

If you are portuguese then you may apply for the ID card in the Consulates.
Or if you have any of your family members residing in Portugal, they may do it for you (with your legalized authorization)
click here (http://www.portaldocidadao.pt/PORTAL/entidades/MJ/IRN/pt/SER_renovacao+de+bilhete+de+identidade+_+sem+apres entacao+do+original+_+sem+alteracao+de+dados.htm?f list=s)