Are you sure about the rate on the loan? 589 x 5 x 12 works out at over £35k, which is obviously quite a bit more expensive. I assume that if the loan was only recently taken out, there is no PPI on it that you could reclaim?
What was the loan for and has anything changed since you took it out? You need to ask for a settlement figure, but at this early stage it will probably be quite close to £28k.
according to www.moneysavingexpert.com/mortgages/mortgage-rate-calculator/
If you remortgaged at the same rate as you have now and added 28k to your mortgage to pay off the loan, the 28k would cost just over 34k to repay, assuming a 15 year term, which appears to be slightly cheaper than you are currently paying, if the monthly payment and term you have stated is correct, rather than your statment that the 28k loan will cost 30k to repay (this sounds a little too cheap).
Therefore, remortgaging the whole lot sounds like a good idea, if you can match or beat your existing mortgage rate over the long term, which may or may not be the case - you should be able to, but 1.99 above base is quite good.
However, you are increasing the amount of money secured on your home, which increases the risk of losing it if you lose an income etc. It is also a little concerning that you have such a big loan, which may suggest a poor handle on budgeting etc.
I would talk to a broker with your exact figures, work out all the sums carefully and possibly do it BUT take it as abit of a wake up call, one off chance to improve your finances and not borrow more while you have the mortgage, because adding debt to the mortgage is the kind of thing you might be able to get away with once, but if you do it repeatedly it can get very messy indeed.