You can doubt as much as you like, but I know a case where the insurance guy pushed for that until he was asked to explain it to the injured guy who they had got to come to the office to meet him. Changed his tune when that happened. Its all a game.
Why should a blameless person get anything less than 100%. Unless of course it pays someone's bonus ?
Because there is no such thing as 100%.
In personal injury claims the claim is in two parts; part 1 - the injury and part 2 - loss and damages.
Part 1 - the injury is usually reasonably easy to settle, and the figures are usually based on past claims. For example you can expect around £15k for losing your index finger, a bit less for middle or ring and bit more for both ring and little finger etc. That's the easy bit.
Then you get to part 2. Now that you have lost your index finger, how should you be compensated? Can you still work, if not then the claim must cover the salary you expected to get for a reasonable amount of time to allow you to retrain for a job where you don't need your index finger. Then there is the time off work while you recovered, the cost of all the take away food because you couldn't cook, the taxis because you couldn't drive etc etc etc.
This figure goes back and forth. Your solicitor will ask for bank statements and receipts - as much evidence as they can get, and then ask for a sum of money. Say £50,000. The insurance company will come back and say "We'll offer £10,000".
This is where it gets interesting. You can choose to push back, and keep this exchange going. If, however the insurance company won't budge, you then have the option to have your day in court where a Judge will decide based on the evidence provided, what reasonably compensation should be. If the Judge decides that the insurance company were unreasonable he might order compensation for £30k. If however he decides that your solicitor has over egged the pudding he might decide that you only get £5k. So you are down on what you would have got.
BUT
Because you pressed to go to Court,
you also get to pay for all of the costs of that. And the Insurance company solicitors will pad their costs as much as possible, just as yours would have done had you won.
A further complication is in the way that you engaged your solicitor. If you are not loaded enough to pay for your solicitor or poor enough that you manage to get Legal Aid, many solicitors will offer a "No win, No fee" arrangement. They take on the risk that they might not win the liability part of the case, but in return you give them an agreed percentage of your compensation...
So now, out of your £20k "win" you end up paying £5k of it to the insurance company for their legal fees plus £2k as a success fee to your solicitor and you walk away with £13000 when you could have had £20k if you had settled*.
*my maths may be wrong here - but you get the idea