LONDON — Each season, the Burberry London collection keeps getting better. For fall, they introduced soft, aged leathers and a Donegal tweed check into their sporty weekend pieces. Color was played up, shown in jewel-toned shearlings, plaids, silk blouses and great cashmere sweaters. Highlights included the knee-length patchwork Burberry plaid skirt, denim trenches and the asymmetric wrap-skirt. Pajamas, pillows, bags and shoes in the signature plaid gave emphasis to the effect.