As a mass employer it is. In 1919 1.1 million men mined 230MT of coal. Twenty years later the same output only needed 750k men and it's all downhill from there. Then there is the squeeze on demand from growing efficiency and the end of steam at sea and on the railway. And above all geology, the coal that was left was deeper, in thinner seams and in worse ground. There is still at least 190 Billion tonnes of coal in the UK, it's just not economic to dig it up.Coal is not doomed as of 1919, for example
Coal employment and output are going to drop, you can manage it better perhaps but the trend only goes one way.
This is where "socio-economic" role becomes a problem. What the UK steel industry wanted and asked for was a few, concentrated, fully integrated works that could produce at volume and remain competitive. But that would have meant major job losses in several key marginals, so what it got was too many sites, all too small to be really efficient and so job losses for everyone when the subsidies had to stop., nor is steel
As has been mentioned above, a British trade union movement that realised the industry had to make a profit in order to exist would be helpful here. Not to absolve management of the blame, they certainly cocked many things up, but if shipbuilding could be dominated by general trade unionism and not craft unionism that would help enormously. Of all the heavy industries this one I think has the best chance.or shipbuilding
Once again though the bulk of the job losses occurred earlier, you can keep the industry healthier by mechanising and automating it faster, but that just accelerates the job losses. At which point we hit the "socio-economic" factors and political interference.; there is a better case to be made for textiles, but that did take until the 1970s and 1980s to fully peter out.
It was only in the mid-1980s that the UK dropped below Japan in terms of manufacturing as a share of total employment. The problem of course was that all the workers were not working particularly efficiently and output per worker was far worse.Further, the wording of the OP ('being as economically powerful as the State of Japan') can be interpreted as extending to Japan's role in 'traditional heavy industry' in the 1980s.
The political problem is that those industries will want to grow in the South East and Midlands, because of logistics, access to supply chains and the available labour force. OTL various governments from the 1930s onwards tried to force those industries to areas of high unemployment and then force them to build lots of small plants to 'spread the benefits'. All this meant was that the industries were inefficient and uncompetitive.There are new industries that emerge in the period in question, such as aviation, aerospace and nuclear, that will be valuable. Along with the automotive and electrical engineering sectors, they can be useful areas for growth.
To go back to Japan, one major advantage/difference is that internal migration was massively more common. In Japan in the 1960s 4 million Japanese a year were moving around the country, about 5% of the population. Comparable figures in the UK was less than 500,000 a year, about 1% of the population. In Japan industry could build in the best sites and workers would go to the boom areas, in the UK people were reluctant to move so government tried to force jobs to locate near them. It is pretty clear which approach worked best economically and I would argue even socially, at least in the medium to long term. Such changes are easier said than done though.