The current account deficit is essentially imports minus exports of an economy.
This is because, in theory, the imports are paid off by the money made from the exports. If the number of imports is greater than the number of exports, then money must be borrowed from other countries to pay for it.*
This money we borrow from other countries has to be paid back with an interest, meaning that, as time goes on, the country will become relatively poorer. It's basically a trade-off of having a really good, unsustainable standard of living now, versus having a lower standard of living but that grows at a sustainable level.
It's basically deciding whether you want good times now, or later. Unfortunately, politicians can't see ahead of the next election, so they only are for the short term, which means that they don't do much to solve the situation.
But, don't worry, the economy won't come crashing down - you're just going to experience slow growth for a very long time whilst other nations, with a positive current account balance whizzes past - they then start importing more than they export from us countries, and it all turns around.
*Borrowing money from other countries leads to a greater demand of your currency. If the supply of money stays the same (so the amount of notes, coins, etc), then cost of the currency will go up - this is one of the causes of currency fluctuation. Obviously, a higher pound will lead to more imports, making it a spiralling problem.