What you need is not a 308, but an AR (or more accurately a 5.56 semi auto of which the AR is the most common)
Keep the 303 for hunting and fun shooting, its a piece of history sportorized or not (my dads fixed up 1903 Springfield is that and there nothing quite like shooting it both for the sentimental and the historical reasons).
I am not overly paranoid (or I don't think so) but Kartrina and the financial meltdonw got me into a piston 5.56 (Robinson XCR actually).
While it is unlikely, what you saw in London, the riots in the US back in the 60s as well as various disasters can lead to a short term social breakdown.
Unless you are well practiced as well as its likely to be short range work. Ergo the need to shoot quickly and with an SMLE it is a hard learned skill.
While the claims are great for it, they were for a veteran soldier with extensive training.
There are a lot of good inexpensive ARs out there (the XCR is not but it is an interesting gun). The Direct Gas Impingement problem in th AR is a myth as an issue in semi auto versions.
Part of the suite should be a good pistol as well. 9mm is as good as 45 these days with good SD ammunition.
Common ammo, I don't count on it. Have an adequate supply (500-1000 rounds for each)
A bolt action gun against people armed with even high capacity pistols at short range is a loosing proposition, ergo the semi auto is a force multiplier.
308 is a fine gun and caliber but its not the best option now.