In recent years, competition has forced lenders to remove clauses which require prior notice. In the case of building societies, the relevant rule can only be changed by 'Special Resolution' of the members. Almost all mortgages are set up on a variable rate basis. Even when the interest rate is fixed for an initial period, it eventually becomes variable at some point early in the term. Rate changes therefore affect virtually all mortgagors.
All lenders have systems through which changes in rate are notified.
This is usually computerised. There are inevitably increases in the volume of letters and telephone calls to financial institutions when interest rates change. Most modern mortgages permit the institution to change the rate without a waiting period. Changes are usually communicated by way of press advertisements. Redemption penalties and interest.