United Kingdom B2B eCommerce Market Size, Share & Trends Analysis Report By Category of Supply (Office Supplies, FMCG, IT Products, Industrial, Manufacturing, Maintenance, Repair, Janitorial and Sanitation), By Deployment (Supplier-Oriented, Buyer-Oriented, Intermediary-Oriented), By Channel (Direct Sales, Marketplace Sales), By End-User (Automotive, Construction, Manufacturing, Information Technology, Telecom and Media, Transportation and Logistics, Retail and Distribution, Others) and Forecasts, 2026-2034