Why are sidestep ILS minima not used in EASA-land? (specific example: EGKK) If you are not aware, London Gatwick (aka EGKK) has a setup with a primary air carrier runway and a backup runway immediately next to it, such that only one runway can be used at a time.

The main runway 8R/26L (South) has full HIALS (ALSF-2 in FAA parlance) with CAT III ILS as well as RNAV (LNAV/VNAV, no SBAS/LPV) and plated SRA non-precision approaches; however, the backup runway 8L/26R (North) only has RNAV and SRA approaches, and no ALS.

Similar runway configurations in the US (KEWR aka Newark Int'l is similar save for having a crosswind runway) allow what is called a sidestep ILS procedure, where the main ILS is flown to higher (nonprecision) minima and then a maneuver is executed on short final to "slide" over to the other runway after visual contact with both runways has been achieved. From AIM 5-4-19:


  5−4−19. Side−step Maneuver
  
  a. ATC may authorize a standard instrument
  approach procedure which serves either one of
  parallel runways that are separated by 1,200 feet or
  less followed by a straight−in landing on the adjacent
  runway.
  
  b. Aircraft that will execute a side−step maneuver
  will be cleared for a specified approach procedure
  and landing on the adjacent parallel runway.
  Example, “cleared ILS runway 7 left approach,
  side−step to runway 7 right.” Pilots are expected to
  commence the side−step maneuver as soon as
  possible after the runway or runway environment is
  in sight. Compliance with minimum altitudes
  associated with stepdown fixes is expected even after
  the side−step maneuver is initiated.
  NOTE−
  Side−step minima are flown to a Minimum Descent
  Altitude (MDA) regardless of the approach authorized.
  
  c. Landing minimums to the adjacent runway will
  be based on nonprecision criteria and therefore higher
  than the precision minimums to the primary runway,
  but will normally be lower than the published circling
  minimums.


Why has the UK not published similar minima for Gatwick's ILS?  The existing OCHs for the secondary runway RNAV approaches are in the 650' range -- if the Newark ILS sidestep minima are any indication, it'd be possible to obtain lower minima for a sidestep approach to the EGKK secondary runway than are currently available from the RNAV or SRA approaches, and it would require no new navaids to be put into service.

Are sidestep approaches verboten in JAR-land? Is there some terrain or obstacle factor that I'm not seeing that makes a sidestep ILS approach into EGKK problematic or not desirable relative to the current RNAV approaches to the secondary runway?  Or can the ICAO/CAA format for approach plates not represent sidestep minima?
You use circling minima for sidestep manoeuvres. While not commonly practiced, they may be requested by the pilot, have done so many times when LEMD (MAD) is in N config, saves 20min taxi-time...