Austin
Innovative, very friendly cars (no aggression at all). Small car specialists. The name makes me think of Minis, Metros, an old green A35 van I used to see frequently when I was a kid, and super-saturated 1960s films where it was always a summer afternoon and all young people were attractive and had cars (or indeed Austin Powers). The colour green.
Also, the Montego Countryman. When I was about 7 or 8, a BRG Countryman seemed to represent the ultimate English, middle-class family.
The Allegro does not conjure up any real negative perceptions: I suppose most of the Allegros I’ve seen have been survivors, so they are not rusty but well-maintained and distinctively different. I never realised they were derided until well after I knew what they were.
Austin-Healey
Summer afternoons in the 1960s (again), speeding through the English countryside or along an Alpine pass. The Frogeye. Friendly, available, attainable British sports cars. Red and green.
Jensen
A car for the jet-set, when that term meant something. Expensive, thirsty with an accent on technology (FF). Quality GT for continental motoring. The world of the 1960s spy/private detective (Rex Carver, The Persuaders, The Protectors). Dark blue or gunmetal. The Healey & GT don't really come into my mental picture, somehow.
MG
As another designer, have to disagree with Barossa about the MG badge. I think it’s an absolute classic, though probably not in the current bulging 3D form.
The name means sporting cars for everyman, less rarefied than A-H, with the common knowledge that MGs are based on equally affordable saloons and family cars being a bonus rather than a detraction. MG is letting your hair down, enjoying free time, cheap, carefree respite from everyday tedium. Colour red.
Morris
Similar values to Austin, but more old-fashioned. I do think Minor, and especially the vans and the Traveller, so maybe the commercial element is predominant. Again, a brand entirely without aggression: completely honest, trustworthy, transparent to the customer. Philanthropy. Royal Mail vans. Colour red.
Riley
My first conscious encounter with Riley as a kid was excitedly spotting an Elf. Seeing a Kestrel and then a Pathfinder at a classic car rally gradually formed an image of a cut-above brand but the sporting edge over Wolseley was not very clear in my mind until later. Colour blue (of course), and that warm grey that a lot of Elves seem to be.
Rover
This is tricky. The perception includes everything from my brother's Series III Land-Rover to my mum's 100(Metro) Ascot to a P5B that a teacher had when I was at school.
Overall, I think the P5-6-SD1-800-75 line represents it best : big, fast, effortless, rugged, distinctive. I include the 800 because a BRG 827 Vitesse, as a kid, was just as attractive as any SD1 Vitesse: as far as I knew, they were both cars for people who had made it - with enough room for their families. A competitive, challenging nature rather than pure aggression. The only car that both the gangster and his trial judge would choose to drive themselves. Brown (walnut, probably) and maroon.
Triumph
The TR7 was cool when I was a kid. A well-worn pack of Top Trumps frequently in use on the school bus featured the TR7 rally car. Unsullied by any knowledge of rust, or industrial action, and reinforced by seeing a lot of Spitfires (usually yellow) some TR6s (usually red), Stags (usually green), Dolomites (usually brown with stripes) and having Triumph bikes pointed out to me, Triumph was a brand that meant fast motoring of one sort or another. The Acclaim (usually cream or some kind of metallic light gold colour) created some mental link with Honda - Japanese technology and reliability : even if that was irrelevant to the rest of Triumph's products, it worked (mentally) for me.
Colours: blue and white. Not sure why.
I’m 22 so most of my early perceptions about marques come from seeing cars in the ’80s and early ’90s, reading car books and magazines from these eras, and talking about them with friends and family, many of whom have always been into them fairly heavily. Also, have done a lot of research in magazines from the ’50s through to the ’70s for a book on a certain other British manufacturer beginning with R, so these attitudes are probably not ‘just’ formed from an ’80s/’90s perspective.