Britain is definitely lagging on the Twitter job posting front so I will do best to stimulate some employer tweeting in the realm. Here is a list of the major British companies doing it already (no recruiters).
By following these Twitter accounts you will get jobs straight from the source and possibly quicker than anyone else. Click on the employer’s name and you will be taken to their Twitter page.
The list is short but growing so please let me know if you find any other tweeting UK employers!