It appears that one needs a job offer to get an (SMC) visa (see related threads), but employers appear to want a visa before they offer a job. Catch 22.
I don't know what the fastest a UK citizen can get an SMC visa, but it sounds like the process can take months if not years. It's not surprising that employers are unwilling to make a job offer until the visa is sorted, but without a job offer it's harder (impossible?) to get a visa (or put in a good enough EOI).
How does one escape from this vicious circle?