I found buying the shares from Self Trade quite straight forward.
I put £125 in our account, this allowed for a price of to 5p (0.07 euro) a share, £12.50 fee and £10 for the certificate. I then rang the given Customer Service number. I did not choose any option and was put through to a Customer Service Advisor. He made the purchase there and then. I told him that I wanted a minimum of 2000 shares and wanted to spend £115 pounds (this included £102.50 for shares and £12.50 fees). I was then told that I had purchased the shares.
I asked for a certificate and they said that they would try to get me one, though I was sent (to my message box on the Self Trade Website) a "Contract Note" which gives details of the transaction, including cost, number of shares and date.
The process was quite simple for me, other than them making a typo in the message they sent to me regarding my certificate, (Euro Tunnel instead of Euro Disney).