Dear Tim Boykett,

if you want to cite GAP, you can do that as follows.

Martin Sch"onert et al.
GAP -- Groups, Algorithms, and Programming.
Lehrstuhl D f"ur Mathematik, Rheinisch Westf"alische Technische
Hochschule, Aachen, Germany.
fifth edition, 1995.

The catalogue of groups is not included in the currently released
version of GAP 3.4.3, but it will be included in the next release
GAP 3.4.4.
Moreover we are at the moment in process of writing up two papers
about the construction of this catalogue. There are

Hans Ulrich Besche and Bettina Eick.
Construction of finite soluble groups.
In preparation.

Hans Ulrich Besche and Bettina Eick.
Construction of finite non-soluble groups.
In preparation.

Best wishes,
         Bettina Eick