Most lenders will allow you to "port" your current mortgage product. By this it means that you can take your existing mortgage with you to a new property and avoid the early repayment charges.
There are a handful of lenders that will allow you a 2nd residential mortgage but will base their calculations on whether you can afford it on your current mortgage + your proposed mortgage and will not make allowances for your payment holiday.
There is bridging finance where a company will lend you enough to pay for your new property by securing the loan on both properties - but this is usually VERY expensive. The rate will be at leat 1% per month plus arrangement fees and will probably mean you incurring the early repayment charges.
If the charges have a short time to run then a lender like Intelligent Finance will be a good bet as they will allow you to buy one without immediately selling the other, altough there is usually a time stipulation of 6 months.