As I understand it this model derived from data for US companies. Is it valid to apply the model as is to UK companies or does it require any modifications?
UK(IFRS) and the US(GAAP) use different accounting standards - off the top of my head you're likely to have differences at least in the Receivables Index, Margin Index, Asset Quality index due to inventory and costing differences. For example LIFO isn't permitted under IFRS, which is going to affect COGS and Inventory. It doesn't mean it's unusable, you'll just have to make sure to convert the statements into a common form. I don't have experience using the M-Score, and I didn't read much past the factors, but I would hope they outline the standard accounting assumptions for each factor.