Beginners metal detecting guide

I want to start metal detecting with a £300 budget how do I start ?

I would say there are a few choices of quality metal detectors out there within your budget
The Deeptech Vista Mini is a powerfull all rounder at £275 it will be a great introduction into the hobby.

Other machines are the :

Garrett ace 250
Fisher F2
Teknetics Eurotek
Whites Coinmaster Pro
Garrett ace 150
Tesoro Compadre
Avoid Chinese machines from internet auction sites and electrical stores.
Always use headphones when detecting, especially at rallies and club digs.
Buy a spade with a long handle, cut down border spades are fine.

Here are some metal detector reviews :
Tesoro Compadre
Deeptech vista mini
Garrett ace 150
Fisher F2
Teknetics Eurotek 

Visit the Deeptech UK sales page

Deeptech Sales Page

Popular beginners metal detectors from Amazon

If you have between £50 and £100 to spend on a new detector !
I'm sorry to say unless you get a bargain second hand machine your in trouble.
These budget machines are childrens toys and will not function as you would have hoped.

Take this small equation into consideration
Lets say you buy a new machine for £80

Second hand value after 1 month £0-£20
Your further interest in the hobby 0-20%

If you buy a quality new machine for £300
Second hand value after 1 month £240-£250
Your further interest in the hobby 80-100%

It's a no brainer !