What you after?
I tend to use online scrapyards. I really don't have the time or patience to actually go to one in person.
I use eBay, search "a3 breaking" or use partshark.co.uk which is a hub where scrapyards upload their current inventories.
eBay is very good in the fact you can search so much so quickly.
I bought my S-Line spoiler through partshark. Saw a burnt out car on there with a mint spoiler on it. Rang up, paid over the phone and 2 days later the spoiler arrived at my door.
Best thing about online is you get access to the whole of the U.K./world as opposed to searching for local places where there's less chance they'll have what you need!