Miracle-Gro All Purpose Compost - 50L £4.25 @ Homebase instore

So they're still £6.99 for one bag then?

Usually £6.99, but 2 for £10 marked on the bags by Miracle Grow makes £5/bag plus the Homebase 15% off = £4.25/bag when purchased in multiples of 2. Also worth mentioning that Wilkinsons sell the same product for £5/bag, but in my case none of the local stores have parking - not great with 10 bags of compost!

Usually £6.99, but with 15% off £5.94 for one bag. But the 2 for £10 marked on the bags by Miracle Grow makes £5/bag plus the Homebase 15% off = £4.25/bag when purchased in multiples of 2. Also worth mentioning that Wilkinsons sell the same product for £5/bag, but in my case none of the local stores have parking - not great with 10 bags of compost!

Cold. There are better deals out there.
You have to buy 2 bags to get this deal so can't get a bag for 4.25.

You can get a 60ltr bag of Jacks Magic for £5 in B&M bargains and they have 3 for £10 in their offers for equivalent size composts - bmstores.co.uk/sea…ost

This is true, but I have gone down the cheaper 3 for £10 route before and found the compost to be aweful! The miracle grow compost gets very good ratings......also worth mentioning that companies sell old compost off cheaply as many of the nutrients are washed out if they sit outdoors in the rain for too long.

That is true but it applies to almost all the current composts on the market including the miracle grow listed. BTW none of these products are actually compost as they are not composted and are only growing medias; the miracle grow a combination of peat, coconut husk, fertiliser and lime.
My preference is Jacks Magic which has a soil element which locks up some of the nutrients due to the cation exchange capacity (I work in soil science) for slow release, but your comment is true and you don't want a soaking wet bag.
Note that when I was in B&M's yesterday all their stock was dry as it is stored indoors unlike B&Q et al.

Thanks for the heads-up, as I need another 10 bags or so I'll check this out. Only slight issue is that the nearest B&M garden centre is 40 mins away.

I'm not advocating that there is anything wrong with miracle grow or the need to go to B&M bargains.
Westland and Miracle grow both make premium products and there is nothing wrong with buying a few good bags for planting around the rooting zone and some really cheap compost for filling under to keep the cost down. You'll have to add plant feed after a few months anyway.
Note that MPC isn't ideal for starting seedlings as the EC is quite high just in case anyone is planning to do this.

Once again thanks for some great info. As this is a very rare opportunity to glean some knowledge from somebody who really does know what he's talking about, please let me know your view on Tomorite grow bags? As I find it a pain to add feed later in the season as it spills over the sides I empty the bags into pots and grow from them. I realise that the main advantage is the 6 weeks of feed added to the compost, but wondered if there were any other advantages to buying this brand?

Just back home, hence delay replying.
I find that the tomorite growbags are OK for their Inteded purpose such as growing tomtoes etc. and have ran growing tials using them but they offer little comparitive improvement over a lot of other MPC products, so I would not expect anything spectacular but they will grow what you want.

It ultimately depends on cost and I would not pay a premium over growbags from MG or WL.

Tomatoes are quite tolerant to medias containing high nutrient dosing and as such growbags are typically multi purpose compost with slightly more fertiliser so it can be sometimes be more cost effective to get an MPC and add fertiliser/ liquid feed throughout the growing season with better results. I didn't quite get your comment about feed but it is quite easy to poke a few holes down into the root zone using a pen and add solid fertiliser that way. Note that I'm sure that you know plants need Nitrogen, Phosphate and Potassium (N, P, K) to grow and all the media discussed contain these but to stimulate better tomato fruiting you want to apply a high K fertiliser relative to N after the first few months planting when most nutrients are spent. A good fertiliser would be a 4-7-10% N-P-K fertiliser or approx equivalent ratio fed after 2 months and then every 5-6 weeks. Most boxes will give application guidelines but it depends on pot size and plants per pot but 3-4 pickles around the root zone should be safe.
Note that composts that advertise feeding past 3/4 months will almost always have controlled release fertiliser but they are typically quite expensive and often less ideal than periodic feeding by the gardener depending on Plant needed.
Note not to go too heavy handed on adding fertiliser as this will pull the pH down requiring lime, a cheap pH tester is invaluable to the gardener. A pH of 5.5 to 6.5 is generally considered the place to be for all but eriaceous plants.
Hope this is of some interest.

Thanks very much for the reply, extremely valuable advice. Really appreciate the fact you've taken the time to explain in such detail!