With a POD that early there are a thousand things you can do to get a truly vast RN. One of the major problems for the RN was it was only paid for by the UK of GB&I, so;
Step 1: Have Imperial Federation with Aus, NZ and Canada sometime pre-WW1 maybe as part of Home Rule for Ireland. You now have 25% more taxpayers (40 million in the UK of GB & I in 1901 plus 5 million Canadians, 4 million Australians, 1 million NZers). While there were some contributions made towards the RN in OTL this will significantly boost them.
Step 2: Counter-intuitively improve relations with Germany and reduce the scale of the German Navy laws. There is still going to be a Dreadnought race but have it slower and less focused against Germany and more general (i.e. including the US, France, Russia etc.).
Step 3: Give Franz Ferdinand better luck. Some kind of general European War is probably inevitable but by delaying it 3 or 4 years you force Germany to switch to an East first strategy meaning no violation of Belgium.
Step 4: With better relations and less of an arms race plus no invasion of Belgium have Britain stay out of the European war and have Germany win a short, sharp war against France and Russia, say in 1920.
Step 5: With France and Russia humbled the UK is both safer, the Great Game in Central Asia is over and its main rival in Africa and South-East Asia is humbled but an emboldened and victorious Germany now has an overseas Empire. In the 1920's Germany is too busy in Eastern and Southern Europe and too tired to start off an arms race but relation deteriorate.
Step 6: 1930: Germany has paid off a good chunk of its war debts and Britain is increasingly nervous about its size, strength and its colonial Empire. There is a rapprochement with Russia and France and increased tensions with Germany. A naval arms race starts. The British Federation (or whatever) only has about 2/3rds the population of Germany (possibly including Austria by now) but its got a higher per capita income, spends more on the Navy and has an Empire to take some of the burden (India and South Africa mostly).
Step 7: Over 11 years the RN completes Plan 1940, a Z-plan like build up resulting in:
BB's
6x 16" gunned alt Lion's
6x 15" gunned alt KGV's
10x 14" gunned, modernized QE's
10x Battlecruisers (no Jutland means more new build battlecruisers)
CV's (inevitable)
6x alt Ark Royals
3x Older 1st Gen carriers
etc.....