This question needs to be broken down, as there are 2 ways this can be interpreted
1) Can I carry two (or more) mortgages on two (or more) different properties?
The key here is, if you can qualify, then absolutely.
There are rules/guidelines when it comes to affordability of payments. If you meet these guidelines, and if you have sufficient assets that, in the case of an emergency, you can fall back on to maintain payments, then most definitely you can have two *or more) mortgages on more properties.
Individual lenders may have a cap on how much you can borrow with them. I.e. not more than 5 mortgages. However, depending on the specific situation, there are always options.
2) Are you able to have 2 mortgages on the same property?
The answer to this is yes, depending on how much equity that you have.
You can have as many as 4 mortgages registered on a property (well this is as many as we have seen, there may be more).
The key here is that the position that a lender is in, is the priority they get if you end up defaulting.
For example, if a lender is in 2nd positon, and the person stops making payments on the 2nd mortgage but continues to make payments on the 1st one, then it is difficult for the 2nd person to set legal proceedings to enforce payment. They would have to see if the 1st mortgage holder will co-operate or help them out.
Being in 2nd, 3rd, 4th position, and so on can be risky for the lenders, so they will charge higher fees and rates.