I'm with Sureterm as well. Just renewed (for a third year). No problems with them (but then I haven't had to make a claim), and they are cheaper than the other companies I tried. Only slight downside is that they are VERY persistent when it comes to renewals -- you may get daily phonecalls (and the occasional text message) as the date approaches.
Definitely check other companies, and be prepared to haggle. Adrian Flux quoted me a higher price, but it was roughly the same as Sureterm's when the legal cover was added. On hearing this, Sureterm offered to add legal cover for nothing AND drop the premium! Now just under £150 for 110 CSW fully comp (3k limited mileage) -- that's with full NCD -- unfortunately I have to include 'commuting' as sometimes drive it to work (pushes up price).
For the record, these are the major policy differences that I noted down, although this is far from exhaustive...
- Adrian Flux policy comes with free legal cover and covers off-roading (on official courses only?) as well as greenlaning; all modifications covered like-for-like; protected NCD included.
- NFU has no compulsory excess; no 'limited mileage' policies -- they don't consider annual mileage nor vehicle value when assessing premium. Legal cover is included, and a basic breakdown assistance (and the cost for additional relay-type cover is VERY reasonable -- well worth considering this in place of your usual breakdown assistance, if more cost-effective). NFU different from other two as they are not brokers: underwrite their own policies.
- Sureterm courtesy car is "a 4x4"; legal cover is (at least) £20 extra; policy covers greenlaning but not other off-roading. Limited mileage policies available. No 'grace' period: when policy expires, that's it, no cover - most policies I've had allow you a 14-day cushion in case you're late renewing.
NFU were more expensive than the other two, but I suspect that I'm not really in their target market. Not much to choose between the others: some of the Sureterm reps are a bit 'hard sell', whereas the Adrian Flux and NFU reps were a little more friendly. All three wanted a complete list of the modifications. Eventually came down to price.
Note -- Although I always compare online quotes for my Pug, and get substantial discounts as a result, I don't bother for my Defender: (i) it is usually difficult to find the correct model, but mainly (ii) they wouldn't provide any kind of off-road cover, and (iii) as soon as you tick the box 'is the car modified?' you'll be directed to ring them to give details.