Better and cheaper than Tumi, but still with lifetime guarantee, is Briggs & Riley. Mainly sold in US, but a few outlets in the UK.
The Work Executive Traveler (style BR 221) fits the BA hand baggage gauge exactly. It includes a laptop bag inside, which you can use separately once at your destination. It is great for the one piece of hand baggage rule.
I got a new one on eBay from LA.