Hmmm:
Wedding number 1:
At the local registry office, with nobody over 30 present (except, possibly, the Registrar) and preferably nobody over 25. Guests asked to wear casual dress, as the bride and groom will be doing. Reception at the local pub (or, if it's Islington, a nice little café with adverts for yoga classes all over the walls). Under such circumstances it might be acceptable to send out invitations via email (or social media).
Wedding number 2:
Either church or registry office but still very traditional, with great aunty Annie and the grandparents attending. Formal dress throughout, with the reception in a posh hotel. For such a wedding, email invitations should definitely NOT be sent out but smart 'fill in the blank spaces' ones, from office stationers, might JUST (and only just!) be acceptable.
Wedding number 3:
Marriage of the daughter of the Lord Lieutenant of the County to the son of an hereditary Lord, in a cathedral with the service conducted by the bishop. Formal 'morning dress' obligatory for the men. Hats obligatory for the ladies. Reception in a stately home (with several marquees). The invitations for such a wedding need to be specially printed, at a cost of perhaps £5 per invitation card.