Seems a system that is quite simple until you start thinking about it, as there will be exception after exception and a huge bureaucracy created to administer it. People do not only make flights purely as leisure trips/holidays.
1. Business travel. Every meeting and sales trip cannot be done at home and via telephone/video. I know there are some who wish it so, but if our companies can't conduct business in the way they want, they will lose out to foreign firms whose governments would not have such restrictions. It is also not possible to disassemble complex machinery, service/repair it, and assemble it again whilst working from home. My brother does this for a living (of British made machinery sold worldwide), making lots of air trips per year in the process.
2. Employment travel. Many UK citizens work abroad, often in places/situations where taking family is not suitable (many in the Gulf, but plenty all over the place). I expect we all know someone like this. They often travel home several times per year for family reasons.
3. Educational travel. Considerable income to British educational establishments (Universities, Private Schools etc) comes from foreign students, many who go home during the three main holidays. Unless this scheme is intended for UK residents only, with foreigners flying in as much as they like, which will really go down well.
4. There seems to be some real jealousy around people with wealth. Many wealthy people will be those taking business risks or positions of responsibility, with the attendant downsides of misjudgement and error. What is the point of taking those risks/responsibility if they cannot buy more or better than those who do not? Sounds quite communist to me. If the buying more or better is outrageously expensive, the rewards for taking risks and responsibility will just get even bigger until the current equilibrium is reached (and a widening of the wealth difference of have/have nots).
5. There are going to be a number of people getting very wealthy on the setting up of 'Flight credit exchanges', seeking out those (many) who have no intention of flying, taking a cut and selling on the credit notes. I would suggest that this wealth 'created' would be better collected through taxation.
If the flight restrictions are only on holidays/leisure journeys, you can be sure that an amazing number of business trips will have a leisure element - indeed I can see a burgeoning business of 'shell' subsidiaries in sunny climes being set up expressly for this purpose!
Without really unwarranted Government intervention in our lives, the only way of reducing air travel is increasing the cost, which will inevitably mean that the poorer sections of the community will not be able to afford it. Thus turning back the clock about 30-40 years?