Hi Dean,
Don't know that wine specifically - but may be able to help a bit.
The wicker capsule may help to date this. I've only seen it on bottles containing vintages 1910 and 1920 but vintage madeira is bottled 20+ years after the vintage date so these were probably bottled in the 30's-40's . HOWEVER it's the sort of thing that might later be copied for sale to tourists in souvenir shops.
The size of the bottle also tends to support the latter - many tourist shops on the island sell 'small' souvenir samples.
The producer/brand is certainly below the radar - may have been just for such souvenirs.
However, on the upside, I have found references to El Rei - but only for Sercial madeira (the driest style) - and that was in a cooking reference.
So indeed it could be 'very old' - but I suspect it wasn't of particularly noteworthy quality and was probably a souvenir - maybe sold as a cooking wine.
Probably little (if any) commercial value. But indeed may have plenty of sentimental value.
El-Rei is, better was, a cheap Madeira blend produced by Blandy. The labels and bottles I have seen so far would suggest that they stopped producing that wine sometime in the 1950ies or 1960ies. The labels would not even state a type of wine (like "full rich") let aside mentioning a grape variety. So unfortunately the bottle and the wine itself have no significant value. Even though Madeira is quite durable, considering the small volume of the bottle and the storage conditions, I would guess that the wine might no longer be pleasant to drink - if it ever was. Sorry there is nothing more positive to say about this bottle
*Wine makes poets of us all!* Hamilton in Silas Weir Mitchell's A Madeira Party.
