If you do not have a passport, or you need to renew your passport, you need to start the application or renewal process immediately. The process of getting or renewing a passport can take up to three months - and you will need to receive your valid passport before you can apply for your UK visa to go to London
The British government requires that your passport be valid for at least 6 months beyond your planned return from study abroad. The government retains the right to deny you entry into the UK if your passport is not valid for at least 6 months beyond your planned return, so make sure to renew it now.
US Students who need to renew or get a new passport should have it expedited. To review procedures for having a passport expedited, they should refer to the US government website. They fall under the category of needing a passport for a foreign visa within 4 weeks.
Students who have already submitted their passport—without having already asked for it to be expedited—can still request expedited processing by contacting a customer service center.
If you are a US citizen applying for your first passport, you must schedule an appointment in advance in order to submit your documents in person at an official passport acceptance facility (see website for locations). It can sometimes take at least two weeks to get an appointment, so make sure to schedule one as soon as possible.
If you are not a US citizen, please check with your country's Ministry of Foreign Affairs for the passport application process and timeline.