Have to say I'd say the same as Demoivre.
If the amount was small I'd say go with with your current option - however E50k over ten years in not an insignificant amount.
Just a quick calculation (not an exact science I know), but assume your current rates and repayments hold then you'll repay c. E71,000 over the ten years.
If you take an equity release (mortgage) over the same period and using a rate of say 5% - you'd repay E63,500.
Against that I acknowledge you don't appear to really be taking a 10 year loan as you intend to pay off in a couple of years time from an expected lump sum, so it may not be worth your while going the mortgage route. Just one point, make sure you opt for a variable rate, or at least a fixed rate of shorter duration than when your expect lump sum.
Best of luck.
BM