The first AST.1238 proposals were intended to be quite complex weapons, either missiles or submunition dispensers. When cost cutting took over in the later 1980s these weapons were abandoned in favour of other, lower performance/cost proposals - Hunting proposed SWAARM and Marconi Brimstone (see SOC's link above).
In the early/mid 1990s further changes post-Cold War/Gulf War etc. led to Hunting proposing SWAARM 2/2000, using Honeywell submunitions and the Swedish/German KEPD 150 body IIRC. I think I have seen patches for these (and the story is told further) in Always a Challenge: An RAF Scientist in the Cold War Years - A First Hand Account by T.H. Kerr.
As far as I can tell, from about 1986 on, Marconi/GEC were pushing Brimstone as a Hellfire derived MMW weapon. They had lost out in the early AST.1238 work to BAe and Hunting so this was their way back into the competition, selling 'low risk/cost' I guess. As time progressed, and Brimstone developed from being just a Hellfire with a MMW seeker bolted on, and came to share only the Hellfire layout (all new inside), I guess the costs and risks went up!
There's a section on the early AST.1238 weapons (such as the BAe AALAAW - http://www.flightglobal.com/pdfarchive/view/1986/1986%20-%202309.html?search=aalaaw) and the rationale for their use, as well as details of their design and testing, in my forthcoming P.1216 book (http://www.secretprojects.co.uk/forum/index.php/topic,6661.0.html - at the printers in the next week or so). AST.410 (which P.1216 was to meet) required their carriage. A surprising amount of work was done on them, more than on SWAARM and the 1980s version of Brimstone it seems.
Attached is a draft appendix from the book that did not make the final edit, showing AALAAW from the Flight article and a derived test vehicle being carried and released from a Buccaneer, ca. 1985.
