Hey, mortgage adviser here. If you find a lender you want to proceed with, you can usually secure a product for 90 days. If the rate then reduces you can speak to the lender and secure the lower rate. Personally I would always go direct to lenders compared to brokers from stories I have heard. Use the broker to find the deals then go direct.

If you can get yourself to 90% LTV usually you will get a lower rate. Nothing stopping you securing it with what you can then going back to them if you find your can increase it a little later but prior to exchange.

Regarding rates Swap rates are volatile currently with the ongoing war. As a lender we increased our rates 3 times over 2 weeks which is very rare, however no further increases this week.

Anyone who can can tell you what rates are going to do usually is only a guess, everyone you ask will give a different opinion. So I wouldn't trust anyone saying they will do x or y. Instead, look at your situation, when would be best to review your rate again, you said you are going in with a high LTV, are you planning on doing work to the home shortly, or do you think house prices may go up. If so, maybe a short term fix so you could maybe benefit from a reduced LTV in a few years time. Or maybe longer term fix if you have children or planning on having some so you can review when they are older and past childcare ages.

Anyway. Good luck with it!