I hope you won't be disappointed, but it is not of meteoritic origin. I cannot be sure without handling the object, but strongly suspect that you have a marcasite nodule (Marcasite is a form of Iron Pyrite, or Iron Sulphide). These formed commonly in sedimentary rocks, and if you live anywhere near the Chalk outcrop, then I'll bet it comes from that stratum. The nodules come in all sizes, though yours is towards the upper range of what is normal. They formed in anaerobic conditions not long after the sediment was deposited, by the action of suphur-fixing bacteria living below the sea-floor. These organisms obtained their oxygen from sulphates, and created sulphide after abstracting the O2. The pyrite quite often replaces or lines fossil shells, though this is frequently unstable, oxidises and disintegrates. The chalk nodules are less likely to break up unless you leave them in damp cnditions with a fluctuating temperature/humidity. A lot of the chalk-derived marcasite nodules have a beautiful radiating golden crystal pattern inside, which you can reveal if you crack them open with a hammer (gently at first). It would have helped identify it if you could report the circumstances of discovery (where geographically and if in fresh rock or on the surface) and provide a scale (ruler is best).
A meteorite, which would be very rare indeed in the UK, generally has some fusion crust on the surface as a result of friction during its descent and if it was not rotating during entry, fluting showing how the fragment was melting during its rapid passage through the atmosphere. Also, stony meteorites are far commoner than iron ones, but weather and break apart quickly in the British climate, which is why most that one encounters were picked up in deserts, where they stand out against the sand and do not deteriorate anything like as fast in the dry conditions.