20 pounds a week, do you know how many bitcoins are? It is less than 0.0018 a week, and if you are going to buy bi-weekly or once per month, it is not even worth it.

The best thing that you can do, is just wait a month, and get $100 - $150, and then use that money to buy some bitcoins, it is not a huge amount of money, but, it is something at all..

And try to get your bitcoins out of coinbase, they had a lot of issues during this week, and their wallet has been offline for more than 12 hours during Tuesday and Wednesday.