They're not available anywhere. Only the 'bare bones' of a case are in the public domain (unless they're reported in by the press, who usually remove court reports from their websites after a short space of time).
(e.g. "Fred Smith, of 42a Acacia Gardens, Sometown was convicted of Assault occasioning Actual Bodily Harm (contrary to section 47 of the Offences against the Person Act 1861) and sentenced to 6 weeks imprisonment").
Even those records are only available from the courts, not via the internet. (There is concern that placing records of criminal convictions on the internet would undermine the provisions of the Rehabilitation of Offenders Act).
Chris