None of the service schedules for my XE require belt replacement and I understand the chain cam is likely to last the life of the engine. However you frequently advise replacing Timing belt

You refer to a 'chain cam' and then a 'timing belt'. I'm not familiar with your engine, but it's got either one or t'other.

If it's a chain cam, then forget about it, as long as you keep it serviced to recommendations. If it's a timing belt, then replace it as recommended.

'Auxiliary belt' would do. They normally drive the alternator, possibly PAS pump, and other mechanical bits which don't have to synchronise with the engine.

If you refer to the Ingenium 2.0 Diesel Engine it's got a timing chain. The chain fitted to these engines from 2015 until 2020 was not great, and failures started occurring sometimes quite early in the cars history. If the timing chain slips or breaks it can and cause irreparable damage to the engine. It was designed to last the life of the engine, but the chain fitted to this engine was sub-standard and it can fail. If you do motorway driving and the engine gets hot and is driven at +50mph for at least half an hour on a very regular basis, then you might be OK for a time. If not the soot and the unburnt diesel dilutes the engine oil and leads to the chain stretching. The plastic tensioners can also fail. JLR recognised this weakness in the timing chain design and did a full recall on the engine in South Korea and fixed the issue. I have seen the recall notice. They failed to take the same diligence, customer friendly, proactive action in the UK.

From 2020 onwards JLR fitted a beefed up timing chain and associated fitting which seem to have solved the weaknesses. However I'll do an annual oil change in addition to JLR's service frequency.

So if you have this engine, listen carefully to it every time you start it up, drive it moderately until it's warmed up and change the oil every 5,000 miles or annually whichever comes first. If you use it just for short trips be even more careful. Alternatively go and get the new model of timing chain fitted. I just paid £1,800 to R&R Jaguar Specialists in south east Birmingham. They replaced all the associated parts as well as the timing chain.

The Ingenium 2.0d engine is fitted to Jaguars, Land and Range Rovers.