I sould have said consumer goods, really. Stuff such as cars and bikes,the british were infamous. Capital goods, they were ok. But just look at a car from the 1970s... cars were much improved during the 1980s and 90s, whatever deficiencies they had could have been fixed. Other industries in the UK went nearly bankrupt at the same time, like Rolls-Royce. The government supported them and they continued to be one of the major manufacturers of jet engines. The french car-makers were nearly bankrupt also, the french governments avoided it and Peugeot and especially Renault managed to recover quite well and become internationally competitive and important.
But what you contest was the need of the common market for Thatcher to destroy british industry. It provided political cover to not intervene in support of those industries. That was what the EEC and the EU now was about first and foremost: political cover, serve as a justification to one's own voters. The UK had to "reorient" towards Europe, hence the old should go. Would Thatcher have done it even without this cover? Perhaps. As you say she had her own political reasons to do it, but I think she'd have met stronger opposition. The role of the EMU, then in planning, must be taken into consideration when looking at how the City developed and took over political influence from industry in the UK. It was the EMU that, in 1990, ended capital controls and empowered the City even further. Would the Uk government risk shifting its country into a bet on financial services if there was no EMU? Remember, at the time capital controls and restrictions on foreign banks were still the norm. Imo it was the anticipation of those rules being rewritten that allowed Thatcher to get away with destroying industry and claiming that the future was services, to sell such a plan to enough tory grandees.
These changes in rules, these treaties, can have big consequences in internal politics. The EMU was the driver of the biggest change in international rules since WW2, and I can argue the political cause and origin of the worst problems in the "western" world today. It wasn't Washington in the driver's seat of the Washington Consensus, it was the europeans...