Level 2.
Level 3 is recommended for properties over 90 years old, or those that have been extended or have had (or you suspect have had) internal walls moved or removed.
You can usually tell if a floorplan looks off by comparing it to other similar ones nearby, or finding out from the seller who will often say 'we knocked a wall down here' when discussing a large room, or an open plan layout, etc.
Level 3 is very extensive; I just had one back that was 132 pages long. It described in minute detail what is normal in that type of house, how the building materials react to things, remedies for issues, and included costings.
I don't think L2 includes costings. My L2 survey a few years back was around 30 pages long, iirc.
If you want them to tell you how much the house is worth, you have to pay extra for either. I was quoted an extra £50 on top of £725 but I've had other firms quote £100 + VAT for just the valuation.
Personally, it didn't seem worth it. The mortgage lender will say 'what is your offer?', they may ask you to provide further info in comments - ours - Virgin Money, did so, through our broker's portal. So I included examples of nearby houses that I knew had recently sold, one we had viewed that was on for slightly more but had an extra floor that had been an HMO and was in very poor condition, and so on. However, I've had 3 mortgage offers in 3 years and that's the first time a lender has given me the opportunity to substantiate why I think it's worth what I offered.
If the lender disagrees, they'll get in touch with you and tell you. If they think it's worth what you offered or more, they'll approve it - with the EXACT value you offered on the paperwork, haha. So - they won't tell you if they think it's worth more. But it doesn't really matter unless you're planning to move within the next few years.
If you're totally new to this, you should expect your lender to want to do an in-person valuation of the house if your LTV is 80-100%. They're more likely to do a drive-by or desktop valuation if your deposit is larger than this.
The best firm I used offered to send me a sample report of a similar property without me even asking after I got a quote. The worst one refused to because 'they're all so different.'