Applying for the YMS VisaYou have to apply online and pay, and then make an appointment to see a person to get your biometrics done (that would be the part in Edmonton). At this meeting you'll have to present a paper copy of your application, your supporting documents, passport, and your passport photos. Make sure you have two passport photos - I only took one because that's what the website said they needed and they made me run down the street to get another set taken. When I pointed out the website said they only require one, their answer was "Oh yeah, that rule changed last week. I guess they haven't updated the website yet".

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After they've checked everything, they will then give you the application BACK to you in an envelope to mail to the high commission yourself. At this point, you can still add extra things to your application - they weren't going to accept my bank statements so I had to get a letter drafted by the bank manager; the interviewer told me just to mail the letter with the rest of the package. I believe you have 14 days from the time you leave their office to get your application to the High Commissioner's office before your biometrics expire and you have to pay the application fee again and start all over.
I did not realize it at the time but this kind of process is very, very typical of pretty much everything in the UK. It takes way longer than it should, involves way more steps/people, and in general is less efficient than a monkey riding an elephant riding a bicycle.
On Arrival in the UKOnce you arrive in the UK, you don't HAVE to do anything - you're not legally required to register with any kind of agency or anything. It is a good idea to register with a GP however, and apply for a National Insurance number. Both processes are free - under YMS rules you don't get NHS coverage until after 12 months living in the UK,
unless you are working. If you're working, you're paying taxes, if you're paying taxes, you're entitled to NHS treatment. You can get work without an National Insurance number, and actually an NI number is easier to get after you're employed. You can find a local GP to register with using NHS's webside:
http://www.NHS.uk.
You'll also want to find a place to live. Take into consideration that most rental companies will want a deposit (aka a "bond"), and first months rent. If you aren't working when you apply for a place, they will also require you to pay all the rent for your tenancy up front once your application has been approved because unemployed people and students won't pass the credit check required for a month-to-month payment scheme.
You'll also want to open a bank account, as a lot of employers require you to have a bank account prior to starting work, but there is already lots on this forum about that.