Just an observation. The JLR "recommended" motor oil for the Defender, and all JLR gasoline vehicles for that matter, regardless of engine (except the BMW sourced 4.4 liter V8), is the Castrol Edge Professional, 0W-20. That oil, according to what is on the bottle only "meets" the JLR specification STJLR.03.5006 and STJLR51.5122. There is no other listed specification, or certification listed on the bottle, or on the Castrol web site. The details of JLR's specification are a mystery. There are allusions on the Castrol web site that imply that this oil meets ACEA C3 standards, but nothing directly stated. For some reason the product data sheets for the oil are not available on the Castrol web site. ACEA C3 is a relatively older standard. The ACEA is a European motor oil standards organization similar to the API in the US.
Interestingly, the first ACEA specification that includes protection for LSPI, or low speed pre-ignition, is C6. The API certifications for the same are API SN Plus, and most recently API SP. Those certifications also include increased protection against timing chain wear and valve guide wear.
As a side note, here in the US at least, every other brand of motor oil lists ALL the certifications a specific viscosity oil meets or exceeds, both manufacturer and ACEA/API. If the Castrol Edge Professional met ACEA C6, or API SN Plus, or API SP, I would expect that to also be listed; it isn't.
Low speed pre ignition is a destructive phenomenon endemic to just about all forced induction gasoline engines. I would find it hard to believe that the engines JLR uses are somehow not susceptible to that. I also find it curious at the least, that JLR would specify a motor oil for it's forced induction gasoline engines that does NOT protect for LSPI.
If the JLR specification does include LSPI protection, it would be comforting to know, but even IF true, why then don't bottles of that JLR specified oil also list the recognized oil certification body certifications that state it?
Something to think about.

 

I haven't gone into the weeds on the JLR OW-20 for the Defender as it's twice the cost of comparable oils for the Defender but I would work on the premise that absence of evidence doesn't equate to evidence of absence WRT LSPI.

If you are worried, steer clear of the OEM oil and go with another brand that meets or exceeds all the JLR criteria for the Defender and does include info on LSPI.

Here is what I and many others use.

Here is info from Liquimoly on LSPI which is a feature of this oil.

 

Only problem with Liquimoly is finding it

 

I guess I'm fortunate in that respect. Not a problem in my part of the globe (USA) It's readily available with Amazon, Nappa and Walmart among others offering it shipped free for about $11/L

 

I tend to disagree with the statement that "absence of evidence isn't evidence of absence". I was finally able to access the product description sheet for the Castrol Edge Professional 0w-20, but could not find a sheet for the JLR variant of that oil. On the generic Edge Professional 0W-20 sheet it states that the oil meets ACEA C5 specifications. ACEA C5 has been superseded by ACEA C6, for several years now. C6 adds protection for LSPI, or low speed pre-ignition, and additionally adds increased protection for timing chain wear, similar to the API specification SP. I then engaged in a "chat" with a Castrol representative and specifically asked what ACEA standard does the JLR specific Castrol meet. The response was specific; The Castrol Edge Professional 0w-20, which meets STJLR51.5122, also meets ACEA C5, which does not include protection for LSPI.

Since this Castrol Edge Professional, or an oil that meets their specification is "recommended" by JLR, it would seem prudent to source and use another brand of oil that meets the JLR specification, and also meets either ACEA C6, and/or API SN+ or API SP for the duration of the warranty period. From posts above, it appears that Liqui-Moly is such an oil brand.

 

It's somewhat confusing and counter intuitive, but STJLR.03.5006 is the newer
spec. The Liqui Moly "LR" labeled "Top Tech 6600" 0W-20 is the correct oil for your Defender.
Liqui Moly 22046 Top Tec 6600 SAE 0W-20 Synthetic Motor Oil, 5 Liter https://a.co/d/6pKH67T

I had them backwards. Full discussion in the sticky on oil changes.

 

I'm a Liqui Moly convert as well. Easier to find that their recommended Castrol spec oil for me too.