Very often, there is insufficient space for several full-size bowls strips indoors. For that reason, a second popular indoor variant called Short Mat Bowls, with characteristics all of its own, has become established with a really big following all over Britain and Ireland. Like many pub games, it is really a miniaturised version of the outdoor game to enable it to be played more easily indoors while keeping as many of the features as possible. It is played on a mat measuring 40-45 x 6 feet with full-size bowls, the mat being easily rolled up and put away for convenience. There is a ditch but this is simply an area marked at the end of the mat with white fenders and to compensate for the shorter distance an intimidating block is placed in the centre of the mat. This makes it impossible for a bowler to aim a fast straight bowl at the jack area - all bowls must use the bias to curl around the block o their target.
More at http://www.tradgames.org.uk/games/Bowls.htm#CrownGreenBowls