No you do not unless your Asthma is so severe that it can cause loss of consciousness, in which case you are legally obligated to do so
You must inform the DVLA if you have a notifiable health condition, but you do not need to inform them of your medication. The legal limit for methadone is 30mg per litre of blood. You should seek medical advice as to whether your dose would mean you would be unfit to drive. Even if you are below the legal limit, do not drive if you feel your judgement or reaction time is impaired.
You must inform the DVLA of a change of engine and provide them with the new engine serial number. A section of you v5 will be made for this purpose.
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Provided that you meet the eyesight requirements with those glasses, you do not need to notify the DVLA.
The DVLA does not notify you when an MOT is due, however you can look up the status of your vehicle's MOT on the government website.
The DVLA (driving and vehicle licensing authority) is responsible for issuance of licenses to individuals in UK. However, you need to be more specific about which cover are you talking about and in which context.
You do not need to take extra tests. If your condition is 'notifiable' you must inform the DVLA and if your medication is on the list of prescribed drugs, you must check with your doctor that your prescription will not put you over the limit.
I think you'd be better off getting in touch with the DVLA and ask them directly - I've never heard of them telling people to get a private licence. The DVLA is the only place that issues driving licences in the UK.
Yes you can, however you must inform the DVLA of the new engine serial number (a section of your V5 is made for this purpose) and you would have to declare the modification to your insurance company.
In the UK, yes. You would need to transfer the registration via DVLA.
yes you need to inform them
The DVLA do not notify owners when their vehicle's MOT is due.