equivalent oil to API CC 15W/40

Any make/brand to the engine manufacture's spec., although I would wait until your local motor factors are open again after the holidays, . .  Halfords prices tend to be fairly steep in comparison.

I don't know what 'deagong' filters are, or who makes them, but if they happen to come from the outfit that took over the 'Crosland' name/brand then avoid them like the plague, . . they're rubbish, and disintegrate in service. 

I think the lack of responses is because it’s quite difficult to find API CC oil these days - it’s an obsolete spec. Morris golden film is probably the best bet, can you get to a Midland Chandlers (or probably many other chandlers) who stock it?

Most of the available API cc spec oils are 20/50.

Morris certainly do a 10/40 CC oil and possible a 15/40 - I can't remember without googling. Although I'd have thought the 10/40 will be fine as the temperature operating window will overlap and our climate will be within spec for either a 10/40 or 15/40.

I'll have a dig about for oil filter numbers for the canaline 42. If quayside if worried about warranty (which he shouldn't) it's the path of least resistance to use the ones he mentioned for the next 18 months. No reason to continue after that time has elapsed.

if you can deign to visit the other side, this was discussed to exhaustion and several suitable alternatives were identified. I seem to recall there was a suitable oil offered by one of the DIY chains.

There are some things not adding up to make any sense in this thread.

In post #1, Quaysider, is saying that his drum of Morris's engine oil has run out, but he doesn't say what spec. it is, only that it was 'golden film'. Later on Nick is saying, correctly, that API-CC is an obsolete spec., so I'm assuming now that this Morris's 'golden film' name is something they only use for oils they produce to the old API-CC spec., . . . it's got to be round about 30 years since it began to be superseded, at a guess, but  API-CC was for normally aspirated diesels, and API-CD for turbocharged diesel engines.

Where things really start making no sense is when 'Quaysider' says there's still 18 months of Warranty left on his engine, . . . if that's so, then the next question is why are you going out of your way to buy and use such an old, out of date spec. of oil in what has to be an almost new engine ? 

Morris have a canny marketing team who produce abd sell quite expensive old spec oils - particularly for the hestric car and boating world.
That said, Morris products are top notch, they have spotted a lucrative market and are the recognised brand leader amongst the group's I mentioned.

Comma, Castrol, Granvilles and a few others still make oils to API CC spec. It's just not so easy to pic a can up in wilkos, a1 car parts, a garage forecourt or whatever.
Bring back the old days, 20/50 for old stuff, 15/40 for mixed humm drum stuff, 10/40 for multi valve and turbocharged petrol engines.
Post mid 90's the range and spec of oils s as vast and bewildering as can be imagined, for what technical merit I'm not totally convinced about. Several specs for different car manufacturers of a 5/30 is a nonsense.

API CC is the spec given by canaline for their current range of engines.

The CC part of the spec is more important than the 10w40.
The CC is an old spec but its more suitable for slow running boat engines than the latest spec as IIRC its a lower detergent oil than the newer spec which is why even new engined specify it. If it was me I would go for 20/50 with the CC spec such as the classic car oil available from wilko.