Hiya Rob.
They were inded a smart looking machine - easy to get at the insides of too, with their removable front and back panels. Although whether the extra ease here is negated a bit by not being able to get in from the top! I dont know.
The picture you posted is of the 18580, from the 1979 series of post purple machines.
The lineup comprised:
15690 top loader
18340 2 button
18380 4 button
18580 4 button variable
18780 Microtronic X2000
The 15690 was replaced by the 15790 and 15792, which saw colouring changes to the facia and an Almond cabinet in the case of the 15792.
The 18340 2 button machine had spin offs, in the form of the 18331 and 18361.
The 18380 4 button span off the 18370, 18371 and 18381, plus 1842 and 1852 Currys exclusives.
The 18580 4 button variable morphed into the 18680, but the only difference was that the outer edge of the facia panel was a bronze colour, rather than dark silver. Compare your picture with the piccies of Lee's lovely example of the 18680, to see the difference.
The 18780 microtronic (introduced circa 1980/81) became the 18880, when the spin speed was boosted from 800 upto 1000rpm.
There were also Microtronic models 18871, 18872 and 18873 which were all 'Superbuy' or exclusives.
Quite why they plucked the last three digits totally randomly, god only knows. Certainly makes it difficult to pick up. Hope the above helps.
Cheers
paul