While I definitely don't think the Tories are capable of organising a functioning national service system, it is possible to do so and many countries do have it. I live in a country with national service, my partner did his service and was trained as a medic (so quite useful). Can train in all different kinds of areas, some which will be of benefit in civilian life (e.g. driver training, medic training, communications etc.) and some giving useful life skills, plus of course benefits to health from all the exercise (something sorely needed by the youth today). Some get picked for officer training and finish as an officer. There's even a sports troop where athletes go so they can continue their sports training while doing their service.
My brother started off doing military service but didn't get on with it so switched to civilian service, where you get a months training in violence prevention, rescue and civil protection, citizen influence, and the environment and society (things that people really should learn) and then worked in a research lab. Flat paid for, all meals provided or food allowance paid, if you rent your own home that you can stay in during the service all costs are paid but if you have to move elsewhere you can get an allowance to cover your rent while you're not there.
The Tory idea of a weekend a month volunteering is ridiculous, there's no time to train them so they will not be of any use. The civilian side would need to be done properly, with training and full time work. And all accommodation and meals would need to be covered. And of course you would need to be able to delay it until after university if you want to.
My son will have to do his service, my daughter possibly, if they change the rules to make it compulsory for women. I have no issue with them doing this, it helps social cohesion, with people from all walks of life working together, and it shows as a very high percentage of the population willing to defend our country. Also its good for networking.