As entropy states, the 1977 strike lasted 9 weeks and the army were used as an interim service.
The last national strike was 2002/3. This was also over pay. This strike was done in periods, so crews would strike for 48 hours at a time, sometimes less. Again, the army was used, with Green Goddesses that were near enough 50 years old. After that strike, conditions were changed for the services, with a new role map being brought in, rank went to roles (a leading Firefighter became a crew manager, etc). Legislation was also changed that put the onus on services to provide fire cover in the event of further strikes and the military could not be used.
Since that strike, there have been local strikes across different services for different reasons. The biggest issue recently was pension changes that the union took to court and won. This is still being rectified at the moment.
The current vote to strike was again due to pay. Over the last 10 years, the highest pay rise has been 2%, with some years being nothing. This resulted in firefighter pay being well below what it should be, having been kept well below inflation rates, etc. Again, crews were offered 2% in July 2022, with this being said to be a final offer. This was rejected and the union started to go down the ballot route. This prompted a new offer of 5% and being told this was a final offer (again). This was rejected as well and the ballot happened, with an overwhelming majority voting for strikes.
On the final day before strike dates were announced, a new offer was received of 7% backdated to 1st July 2022 and a further 5% from 1st July 2023, which was accepted. This was achieved without stepping out the doors once. I'm led to believe services had no contingency in place for the strikes, which put pressure on the government to sort it out. We are not the only service going through this, with quite a few government services currently taking industrial action.