If you are living in the UK, you have been able to apply and pay for a new Passport online for over a year. But that process still meant that you had to visit a photo-booth or a studio for the two required photographs which you include with a printed copy of the online application and your old Passport and send off to the Passport Office. Not any longer. The Passport Office now accepts photographs taken on a mobile phone or digital camera and its website now has amended information to help you prepare ones that are acceptable. You must still send the Passport Office your current Passport - they won't process your new one until they receive it - but this should speed the process. This change does not apply to applications from abroad, to first Passports or childrens' Passports.
also--be very wary if you renew online--i fell into the trap of being conned into using a checking service...their website looked just like the passport service. it was only when i paid the fee it was stated it was a checking service--and it was non-cancellable.