Not in the UK you don't - a basic PPL can fly IFR (provided they remain VMC).
True. The UK is a bit odd in that respect. You can indeed fly IFR on a PPL, but in that case it's more a state of mind than anything else, since the IFR ruleset is more restrictive than the VFR ruleset, you're not allowed in IMC and you don't get any more/better access to controlled airspace than VFR anyway.
Additionally, of course, the UK (still) has the IMC rating, allowing you to fly IFR/IMC in certain classes of airspace.
But as the OP is from Brazil that's not all that relevant.