Your chances of success in a legal career are roughly the same whether you obtain a degree in law or a degree in another subject and a PGDL. Your chances will be enhanced by doing well in any subject at a competitive university.
There are pros and cons to both routes. It might be best to follow your instinct as to which subject you most wish to study at university (in your case, English).
The pros of studying law as an undergraduate are as follows -
(1) You may find the law to be a very interesting subject, because it is.
(2) If you become a practising lawyer, and especially if you become a barrister, your greater depth of legal knowledge may assist you in your first few years in practice. Thereafter, the people with PGDLs will have caught up and will know as much law as you do. For the first few years, they are cuffing and bluffing it, but "BS baffles brains" is the motto of all self-respecting lawyers (and most Judges, obvs - the only people who take this stuff seriously are Law Dons, and also Lord Burrows in the Supreme Court, but he's a Law Don).
(3) A law degree opens a path to a career as an academic teaching and writing about law.
(4) You save on one year of fees and expenses because you won't need a PGDL.
The cons of studying law as a undergraduate are as follows -
(1) You may find the law to be a very boring subject, because it can be if you are not in the mood.
(2) Those precious undergraduate years will not come again, so why not spend them studying Akkadian, Physics, Art, or Geography, if you love one of those things? Doing so will enhance your life forever, and may even make you a better practical lawyer in the long run. Also, you have an easy option to abandon law and make a happy career of whatever your first love is. BTW, anyone who wants to practise in Hard IP (Patents and Trademarks) should seriously consider a science degree.
(3) If you are at a university where social life is mainly faculty-based rather than a collegiate university, you won't be driven bonkers by your fellow law students being boring and/or stressed out and/or all thinking that they are Elle Woods' hotter and smarter little sibling. At a collegiate university, you can safely ignore all of the other law students except occasionally your tutorial/supervision partner and the bunch of losers from that other college whom you beat up in the moots.
(4) Another year of fees and expenses is no biggy when looking at a career of several decades in which, if things go well, you stand to earn the big doubloons.
Approximately half of the lawyers in the UK have law degrees and the other half have degrees in something else.