The thing is, the Landlord is entitled to raise the rent. It is possible to do this as part of a rolling tenancy (if terms are built in) or to offer another fixed term tenancy rather than just rolling it over and increase the rent with the need tenancy.
It is normal for Landlords to raise rent and you should expect it to happen sometimes. It is an area you can negotiate about, so until you’ve done that, don’t assume the final resulting rent will be loads more than you pay now. Often LL will ask for a rent increase but faced with a. Tenant moving out, will compromise. Remember, that the LL might get £50 per month moreover month, but if there are voids after you move out and no tenenats, it can take over a year to recoup that lost month of rent, plus often LLs need to spend money in maintenance before a new tenant is advertised for. So, don’t assume you won’t be able to stay for the same or very similar rent.
The offer of a new fixed tenancy and rental charges is the start of the negotiation. If you don’t accept it, at that point the LL will have to give you notice to quit and the 6 months starts from then......so you aren’t going to have to exit anytime soon and your existing rent will apply over the notice period.
At the moment, I don’t think you’ve actually had new tenancy agreement or rent increase actually given to you. Don’t assume the worst case scenario and that there will be a massive hike or you are about the lose your home. You could be there for years more.
Most LLs won’t want to end the tenancy of good, reliable, paying tenants to get £50 more per month. The costs of tending the tenancy are far more and can take years to recover. If there have been other issues with you as tenants, they might be keen for you to move on....but the normal notice periods will be required and at the moment, even from the first point you can actually give notice, it’s 6 months due to Covid. And then sometimes tenants still don’t go for a variety of reasons and an eviction order can take mo this and months. You could be there a very long time.
The key is to think if you wish to stay and how much you’re prepared to pay. And then when the LL approaches you, have a constructive conversation about it.