You cannot play NTSC-U (American) Wii games on a PAL (UK/European) console natively. The Wii enforces hardware-level region locking.
Proceed at your own risk. These void warranties and can brick the console.
Owning a physical game disc generally permits personal backups in some jurisdictions (DMCA exemptions vary). Downloading ISOs you don't own is piracy.
Bottom Line: For a hassle-free experience, purchase the correct region version. Softmodding is viable for enthusiasts but carries technical risk.