How to get a passport
You will not be able to board a plane, boat, train or anything else that takes you abroad without having a valid passport in your hand. If you're leaving the country it's the only item you absolutely have to take with you. Adults and children need their own passports and they can take up to 6 weeks to arrive for new applications and 3 weeks for renewals. This can take longer if there are any errors in your application.
Even if you already have a passport some destinations (including Mexico, Singapore, China and Thailand) insist that you have at least six months validity remaining before you enter the country. So before you book to go anywhere check the requirements and get it sorted! The Foreign Office lists all countries so head to the website and select the 'entry requirements' option.
If you need a new passport your first point of call should be the UK passport office where you can apply online or look at the paper options, they also give information about how to get a passport urgently.
Make sure to go through your application with a fine tooth comb as any errors can cause delays and more faffing around! Also, If you need a countersignature, think carefully about who to use. It is likely that the passport office will contact them using their work address so, for example, if you ask a teacher make sure school holidays are not coming or don't ask someone who is about to travel themselves.
Top tip: once you have your passport take a photograph of both pages which show your photograph and details, and email it to yourself. You should then be able to easily access the details if you need them or if you lose it.