well yeah cause someone has let VM skip by their congestion issues and got away with national skewed averages. But still cable isnt available everywhere.
Thinking about it some more I would do something like this but isp's would fight tooth and nail against it.
1 - No speed at all shown on product page if no postcode/address data entered. Only other specs of product such as usage limit, bonus features etc.
2 - After data is entered, expected speed is shown, for tech's like FTTP and cable where the only variable is congestion, then peak time speeds are shown for average for the localised area, e.g. the node. For DSL services a estimate is provided internally, then checked against peak time performance, if no expected congestion the estimate (minus overheads) can be used, otherwise its reduced further for expected peak time congestion and then that value shown to the end user.
3 - There can be a note provided in smaller text saying that during off peak hours speeds may be faster and up to the max burst speed of the product, for DSL the line estimate would be placed there, for FTTP/cable it would be the connection speed so e.g. gigabit/sec.
Finally the regulator would add an "automatic" compensation scheme to discourage abuse of the system, if a customer proves the expected speeds are unrealistic they are automatically refunded "double" the value of their contract. This also discourages longer contracts to a degree as a longer contract would of course be a higher penalty for failing to meet speed expectations. The system in place for proving failure could be a video clip showing ethernet speedtesting on a mutually approved speedtester such as one hosted by ofcom, failing to get within 10% of the expected speed 3 times during peak time hours with tests at least 10 minutes apart, indicating the subpar performance is lasting for sustained periods.
Downsides I already know, added complication of calculating localised speeds, customers could abuse this, effort required to get the refund might be considered excessive for lazy people, the speedtester used needs to be reliable. No osolution is going to be flawless, there is always going to be things people wont like about it, to me a solution is something that puts fears into the mind of the isp, something that encourages investment to get higher advertised speeds. Also the way national advertising on tv, in newspapers etc. would not be affected by this and be a separate issue. To help combat issues on those platforms, things like Fibre need to get banned in hybrid broadband adverts. Which we now have a pending court case for because the ASA cannot do its job.