I have just had a failure in the same way with a very expensive Bristan bath shower mixer (about £350) out of waranty. This occurred on a Saturday evening and lead to the need to have my mains supply turned off until I was able to get and fit an isolation valve to the bath supply pipe!
I visited Plumbase, on the Monday, in an attempt to obtain a replacement for the failed component. The component which failed was the rubber retaining ring,the thing that holds the two pieces of the ceramic valve in place! This is effectively the same thing as the washers found in old taps, however it does not function as a seal in the way a washer did. It is more like a spring which keeps the two pieces of ceramic in close contact with each other. This website shows how to service this type of tap... www.diydoctor.org.uk/projects/ceramic_disc_taps.htm the failed component in this case and I suspect Alan's is marked in photo 2. as "A" "Disc retaining washer"!
Plumbase told me that I would need a new (complete) valve cartridge to fix the problem which they did not have in stock. the reason they gave for not having stock of replacement valves was that they are not a generic component and that almost every tap has a different size valve body and that in most cases, it would also be necessary for them to carry twice the number because hot taps are left handed whilst cold are right handed! They said that they could obtain the correct replacement valve but would need to know the specific model number in order to do so! For this particular Bristan Tap range, the two valves for the bath shower mixer were quoted at £45 each and the valves for the basin taps would be £30 each. It was not possible to obtain a replacement for the failed "Disc retaining washer" A few pence if obtainable!
I contacted Bristan hoping that they might be able to supply a bag of these little rubber rings but was told they do not supply them and that the only way to repair the tap was to fit a new valve! Not in warranty... at my cost! All of this has taken over a week and still have no cold tap on my bath!
This story gets worse!!! While I was waiting for an answer from Plumbase I became worried about my Kitchen mixer £180 which is made by "Swirl", this is a brand of "Watersmith uk. ltd. owned by Screwfix. This company is not contactable, all attempts to contact them online take you to Screwfix and there is no Tel. no. for "Watersmith" listed. Screwfix told me that because the tap set was over one year old (out of warranty) If it failed I would have to buy a new set, they told me that they did not and would not supply any component part for it.
Warranties, see under fit for purpose, this website... http://www.tradingstandards.gov.uk The sale of goods act states that retailers, by law must give 6 year guarantees on all goods and that parts must be available for a minimum of 10 years depending on the amount of time a product is deemed to be expected to last!
It is generally held by the trade that a newly fitted bathroom should be good for 20 years, few people would change toilet bowls baths shower enclosures basins etc in less than 20 years and these items are usually guaranteed for 20 years! Therefore the fittings, taps showers etc. would be deemed by the consumer protection laws to only be considered "Fit for purpose" if they last a comparable time!
This is intended to be a cautionary tale, and unless we as British Citizens actually start to force companies to comply with these laws, my advice is to not buy expensive taps from companies such as Bristan and don't even consider buying taps from Screwfix unless they are at a price which is low enough that replacing them every few years is acceptable. I have found that there are many places where almost identical taps can be obtained for as little as £40 cheaper than Bristans replacement valves! Consider buying a spare set at the time which will provide sufficient spares for any components which fail during the "fit for purpose" duration and will still be considerably cheaper than buying an expensive set!