A number of blue-chip UK shares have rather juicy yields right now. As an investor, I like to keep my portfolio diversified. But I think for a £20K Stocks and Shares ISA, spreading the money across a handful of carefully researched and chosen blue-chip shares could give me the diversification I want. Here are the five shares I would choose. My first choice would be a long-term high-yielder: British American Tobacco (LSE: BATS). Why is the share high-yielding (9.9%, to be specific)? The answer is a combination of decades of annual dividend rises, combined with a falling share price. Over the past five years, this UK share has fallen 19%. That reflects a very real risk: declining cigarette consumption in many markets. Less cigarette smoking could lead to lower revenues and profits. Still, the cigarette business remains substantial, despite being in decline. British American has a portfolio of premium brands like Lucky Strike I think can help it build business beyond the cigarette format. Its cash generation remains formidable. There are lots of financial services firms with high single-digit percentage yields I would happily own in my ISA. I would not want to concentrate my holdings too much on a...