Hi bricksguy
Plan A - pay off your home loan "so that if problem occurrs with buy to lets my own home may escape the banks"
I don't think that will work. If you are unable to pay your buy to lets, then the bank will repossess them and register a judgment against your home. So that is not a reason for paying off your home loan.
Plan B - Keep your cash in case you need it to retain your trackers
I think that this is a better plan. Let's say that interest rates rise, a tenant doesn't pay for a few months and you fall into arrears. The bank will exploit this opportunity to try to get you off your tracker. If you have a cash reserve, then you can meet your repayments and retain your tracker.
If you run out of your reserve, you will probably be able to get a payment holiday on your home loan repayments to fund your buy to let repayments.
There is also a possibility that the lenders will offer people deals to come off trackers or will give them some incentive to pay capital off their cheap tracker. So keep your cash available for this.
You mention that you have "a few buy to lets". If you have high borrowing, then you should consider selling a property and reducing your borrowing accordingly. This will reduce the risk. However, if you have cheap trackers, these are probably very profitable businesses and maybe it's less risky to retain them as the profit will reduce your overall negative equity.
Other issues
Building up a cash reserve is the most important consideration. When you get to a stage that you are no longer worried about arrears and losing your trackers, it is usually correct to pay off your home loan before your investment property. You get tax relief on 75% of the interest paid on the investment property mortgage but no tax relief on interest paid on your home loan. As the interest rate on the investment property might be higher than on the home loan, you will just have to do the calculations.
Case study
It's helpful to list out all the details in a Case Study format as it may give rise to other issues. There is a very interesting case study of someone with multiple buy to lets and some cash wondering which one to pay off. Unfortunately I can't find it at the moment. You might check through the threads yourself. It sets out a lot of the issues you have and a few of us gave our different opinions on it.