DIY St Johns Wort Tea?

Seems like I'm not the only one who loves St Johns Wort tea - my usual retailer is out of stock!

So I was wondering, can it be grown in the UK and then used to make tea?

Found some seeds here: http://www.ebay.co.uk/itm/Herb-Seeds...wAAOSwCypWm9op

Anyone tried it? How long would it take for it to grow big enough to be useable?