If you ever come to the UK, a quick wander around the suburban areas of any town will provide you with the answer as to where all the steel came from.
A typical house in a UK street has a low brick wall at the front of the garden topped off by large sandstone coping stones, this is about the height that you could comfortably sit down on. Prior to WW2, most of those coping stones would have had wrought iron railings set in them up to about five feet in height, and if you look at most of them these days, you can see little stubs of metal at regular intervals inset along the top of them where the railings were sawn off or cut off with a torch. My house (A large Victorian one) has evidence of this for example. Most iron gates went too, and you rarely see an original pre-war iron gate on a residential property in the UK.
If you add that all up, all over the UK, thats a hell of a lot of metal, and this was supplemented by 'drives' for metal at regular intervals throughout the war, with people handing over cutlery, pans and all kinds of bits and pieces. So steel was not really an issue, of far more strategic value was the bauxite in France, which was a major component in lighter aircraft alloys.
With regard to shipbuilding, most of the UK's shipbuilding industry was on Tyneside and in the ports up near Scotland, although it did have other industrial bases, a lot in Ireland for example and some near Liverpool, but the vast majority was in the north of the main island, which meant that it was largely out of range for aircraft with heavy bombloads, regardless of whether they came from the European mainland or across the North Sea from occupied Norway or wherever.
The bases at Portsmouth and Devonport did have some building facilities, although they were more about servicing things than building them, so pretty much anything could be built safely out of range from major bomb raids if necessary (keep in mind that German bombers at night did not fly in formation, they each navigated to the target individually, the navigator being the ranking guy in the plane as opposed to the pilot in most cases, so they lacked the advantage of blanket damage from tight formation bombing along the lines of the USAAF), and even if bombers made it to Scotland, bear in mind that they usually had to navigate at night, which meant that only really recognisable inlets of water offered practical targets, which is why Liverpool, Manchester and London copped many more raids than the heavily industrialised midlands, as the bombers could not fly up a river to find their way to targets in the Midlands, which they could with the readily recognisable (at night) Mersey and Thames Estuaries (although the Luftwaffe did have pretty good maps of the UK, as it was photomapped by Lufthansa prior to the war). The Luftwaffe did use some radio navigation aids to assist in night navigation for bombing (such as knickbein - where two widely-spaced radio beams would be aimed to intersect over a target) but it was not suitable for the kind of pinpoint accuracy you'd need to knock out a ship on a slipway.
On top of all that, most of the big RN Battleships were already built before the war, and the RN had a very big fleet in those days.
Chock