Changing The Term of A Mortgage After It Is Taken Out

I am buying a new house, but am unsure what term to take it out over. The LTV is low. I can afford to take it out over a 10 year term (I am aged 44). However, if I subsequently want to lengthen the term of the mortgage to say 20 years (to have more disposable income if circumstances change in the future), is this generally a problem? Can you just say "I want a longer term, no reasons specified" or do you have to demonstrate financial distress before they will lengthen the term of a mortgage?

The lender is ulster bank, and I meet their 2016 mortgage lending criteria for up to a 20 year term.

Go for the longer term and pay the payments for the shorter one, then it will finish in 10 yrs if nothing changes. Not always that simple to extend a term, definitely not just a case of saying you want it.

Only downside to this plan is you will have to take life cover over the 20yr term rather than 10 so will cost slightly more.