I think you need to look more tward a consumer law forum as the advice here would not be grounds for your case with Candy (Haier)... that said..

Please note: this is general guidance only. It is not intended to be, and should not be taken as, legal advice. For formal advice on your specific situation you should consult a qualified legal professional.

The OPSS safety alert was issued in May 25 - candy heat pump dryer and others.  Owners advised not to use.

Follow up in August 25 - insufficient repiar - requirement to warn notice to Haier was issed saying the earlier modifcation was unsatisfactory and still unsafe.

How did they get on the market?

• UK/EU law (at the time of manufacture) – Domestic appliances such as tumble dryers must comply with the Low Voltage Directive (LVD), the General Product Safety Regulations 2005 (GPSR), and the relevant BS/EN safety standards.
• Conformity Assessment – The manufacturer is responsible for conducting conformity assessment, maintaining a technical file, and affixing the CE mark. Unlike gas appliances, many electrical appliances can be self-certified — the manufacturer tests them against standards (often in their own labs or via third-party labs) and signs a Declaration of Conformity.
• Type/sample testing – There isn’t necessarily a government-run “type approval” scheme. Compliance is usually demonstrated by a mix of in-house testing, supplier certification, and sometimes third-party certification (e.g. TÜV, Intertek, BSI).
• So yes, these machines should have been type tested/sample tested — but enforcement relies heavily on the accuracy and honesty of the manufacturer’s testing and declaration.

Why the first repair wads later deemed unsafe

• From what you say, the “modification/repair” (retrofitted safety kit) did not actually resolve the underlying hazard.
• Government intervention (via the Office for Product Safety and Standards, OPSS) suggests the company’s first fix was either not compliant with the original standards, or introduced new risks.
• The company’s excuse of “new standards” is a red herring. If there were no new EN/BS standards, then the issue is continued non-compliance with existing law.

Why the secrecy?

• That is not a valid justification. Manufacturers often say this to avoid liability exposure, but legally, consumers and regulators are entitled to know the nature of the hazard.
• The OPSS database of product recalls normally includes a plain-language description of the defect (e.g. “fire risk due to lint build-up and faulty connector”).

https://www.gov.uk/guidance/product-recalls-and-alerts

So to answer your questions directly - in my personal opinion

• Yes, they should have been type tested/sample tested.
• They should not have been placed on the market if they failed the applicable standards.
• After one failed “fix”, a replacement or refund is the proper remedy — not an endless cycle of retrofits.

Please note: this is general guidance only. It is not intended to be, and should not be taken as, legal advice. For formal advice on your specific situation you should consult a qualified legal professional.

Let's start with the primary question - yes they would be subject to a type test to be declared compliant with the applicable manufacturing standards harmonised or designated permitting the application of CE (or UKCA) marking.

ALL standards are based upon consideration of "foreseeable" use and with respect to this type testing of white goods performance is like a car manufacturer mpg based upon "unreal" laboratory conditions.

What has become appparent is that over time the clothes being put through such machines have changed, the manner in which we wash clothes has changed and the maintenance regieme (operating instructions issued) have not kept pace. The first time this issue erupted was due to a build up of fabiric fluff around the element that heated the air used to dry the clothes.

Part of conformity assessment (CE / UKCA marking) is to have a process that when significant problems are identified these are communicated to the purchasing public including if necessary a full product recall.

This issue with clothes dryers is why the UK now has an Office for Product Safety & Standards who oversee matters of product safety including communication of issues and recall.

There is a fundamental design issue with all clothes dryers - they have heating elements which can over time become coated with flammable fluff which if allowed to accumulate could ignite.

A professional laundry has in place a procedure to regularly clean the inside of dryers from their industry experience of fires. In the domestic market we have ignorance of what happens with others - this is where lobbying primarily by the London Fire Brigade launched the OPSS.

Your manufacturer is being vague because there is no direct and definitive answer to the issue and any change of design (switching parts) needs to be checked. As you have pointed out the supplier has attempted a "fix" for the original issue which the OPSS has now determined to be wanting which merits a revised approach.

Vauxhall took two attempts to correct a faulty part in their Zafira B which also caused fires.

Samsung took a significant hit globally withdrawing the Galaxy 7 due to an exploding battery.