We investigate factorisation at small x using a variety of analytical and
numerical techniques. Previous results on factorisation in collinear models are
generalised to the case of the full BFKL equation, and illustrated in the
example of a collinear model which includes higher twist terms. Unlike the
simplest collinear model, the BFKL equation leads to effective anomalous
dimensions containing higher-twist pieces which grow as a (non-perturbative)
power at small x. While these pieces dominate the effective splitting function
at very small x they do not lead to a break-down of factorisation insofar as
their effect on the predicted scaling violations remains strongly suppressed.Comment: 17 pages, LaTeX. Updated version corrects some small misprints and
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