UK: Photo pricing examples. Stock pricing vs. full commercial license

[tuxellie]

I unintentionally put a small image on my website that was discovered by one of Pixsies scanners.
They sent me threatening emails and wanted to press £500 out of me.
The image was removed immediately and I responded with links to examples of similar images on stock photo sites. Pricing for online use was in the range of £20-70. I offered to pay this amount.
They insist on the price of a "full commercial license".
I did some research on the web and found that in UK copyright law the so called "user principle" is often applied. This means that the court takes into account what the defendant (me in this case) would have done if he or she would have acknowledged that a license for an image needed to be obtained. In my case I would have never purchased a full commercial license, but either picked a cheap stock photo or used an image that is available for free.
So my question is how are my chances to argue with the "user principle" and insist on the prices I suggested ?
I want to settle this, feel reluctant to support this questionable business model by paying up and I do not want legal overkill and court costs.

[DavidVGoliath]

In UK copyright claims, case law has established that it's the reasonable fee that a willing seller and buyer would agree to - and specific case law will favour the seller in the event that they can substantiate the grounds for their licensing rates; the Intellectual Property and Enterprise Court made a ruling that would serve as a yardstick back in 2013 (see http://www.bailii.org/ew/cases/EWPCC/2013/26.html, particularly parts 13 and 22)

Once you've read the above, you may come to understand that even if other websites offer similar images for far lower fees than you are being asked to settle for, if the specific image commands a higher fee (and, for veracity, if the seller can prove that such higher fees have been paid in the past) then that's more or less how the courts will rule. Judges tend to look to past rulings as the foundation of their opinions, as this is far easier than establishing new precedents.