Does this look like magnesium deficiency?

Found this about magnesium deficiency (my highlights)

Magnesium deficiency
Symptoms: Yellowing between the leaf veins, sometimes with reddish brown tints and early leaf fall. Magnesium deficiency is common in tomatoes, apples, grape vines, raspberries, roses and rhododendrons.

Cause: Magnesium is needed for healthy leaves and for plants to harness energy from the sun (photosynthesis). Soil shortages of magnesium are more common on light, sandy soils. Over-use of high-potassium fertilisers (such as tomato feed) can cause magnesium deficiency, as plants take up potassium in preference to magnesium.

Remedy: In the short term, apply Epsom salts as a foliar feed in summer. Dilute the salts at a rate of 20g of Epsom salts per litre of water (1/3oz per pint) plus a few drops of liquid detergent. Apply two or three times at fortnightly intervals, spraying in dull weather to avoid leaf scorch.

In the long term apply to the soil around the roots either Dolomite limestone (calcium-magnesium carbonate) at 100g per sq m (4oz per sq yd) or Epsom salts (magnesium sulphate) at 30g per sq m (1oz per sq yd). Dolomite limestone will make the soil more alkaline, so should not be used around ericaceous (acid-loving) plants such as rhododendrons or camellias, or where the soil is already alkaline.

H*meb*se sells it, is there one near you? https://www.homebase.co.uk/epsom-salts-1-5kg_p407243

Doesn't look right for deficiency to me - could easily be raspberry mosaic - no harm in trying some Epsom salts, if that doesn't fix it you'll at least have narrowed down the list of possibilities.

Ack, yes, it does look a lot like raspberry mosaic now I Google it

Well, I will give the epsom salts a go, but if it doesn't do anything, it may be curtains for this raspberry. The newer leaves look healthy. Is there any benefit to just cutting back the diseased parts, or will I need the whole plant to go in the hope of saving my other two plants?

If you decide its infected, best to dig it up and bin it - can't remember for sure off the top of my head, but I think this is one of those viruses which are transferred to other plants by insect pests.

Chemists sell Epson salts but tell them you want it for the garden otherwise they'll try to sell you other products to treat constipation.