//You could argue the current lockdown discriminates on disability grounds in that tighter measures (shielding) apply to those with diabetes, heart problems, dementia, etc.//
We need to me a bit careful between "advice" and legislation. There is nothing in the legislation which differentiates between any group. The "do not leave home without a reasonable excuse" section applies to everybody. However, vulnerable groups (which includes the over 70s) have been advised to take extra precautions.
It is not clear from the Grauniad article what is being proposed. It mentions "beefing up protection" (whatever that might mean) for the over 70s and other vulnerable groups. It then goes on to mention a number of options that are being discussed. They add to the number of "cigarette packet" ideas that have been discussed.
Over 70s are not any more susceptible to contracting the virus. They are more likely to suffer serious symptoms or die if they do. Similarly they are no more likely to pass it on to anybody else. The idea of the "lockdown" is to slow the spread of the disease and so avoid the NHS being overwhelmed. That has, apparently, been achieved. The "Nightingale" hospitals in London and Birmingham are being mothballed (although for some reason one in the North-East is about to be commissioned).
My view is that if (say) the current legislation (S6 of the Health Protection (Coronavirus)) regulations are eased for those under 70 but maintained for those over that age there will be widespread ructions. As I have said before, the country is going to have to learn to live with the virus and not labour under the misapprehension that it can be contained. Part of that learning is not to discriminate against people simply on the basis of their age.