So, what is a MAC code?

A Mac has nothing to with fast-food; MAC stands for Migration Authorisation Code. It is issued by your existing broadband provider and is used to seamlessly switch from one provider to another without having to wait weeks to cease your line and re-register with another provider. It is usually about 17 character’s long, you do not have to worry yourself with the bizarre format.
How do I switch from one provider to another provider? It's easy to switch, all you have to do is
1. Obtain your MAC Code from your current broadband provider. This is normally achieved by calling their cancellation line and you should receive it in less than 5 working days by either email or a courtesy phone call. 2. Contact your new provider and register your Mac Code with them.
3. After registration you will receive a confirmation email or a confirmation snail mail with further detail as to when the switch will occur. The switch will usually occur in 10 working days from the date you registered. Do I cancel my account with my current broadband provider? No! It is important you do not cancel your account with your existing broadband provider. If you do, you may be without broadband for several weeks.
Can I switch from any Internet Service Provider to any Internet Service Provider? You should be able to switch from all non-cable broadband providers. Will my MAC code expire? Yes, MAC Codes do expire. You must use it 30 days from when it is issued
What do I do if my Mac Code expires?
It will no longer be valid. If your MAC code does expire you will need to call your existing service provider and ask them to re-issue you another one.
What to do if your existing Broadband Provider refuses to issue you your Mac Code?
If you’re existing Broadband provider refuses to issue you your Mac Code, then log a formal complaint with the Telecom Watchdog Ofcom on 02079813040.