Wandering around the garden a few days later, I discovered that the pigeons had appreciated my hard work and left me a few thin shreds of stalks as a thank you present.
Mr. P helped me erect "emergency protection" in the form of chicken wire and told me that they might "bounce back." I wasn't so hopeful and muttered darkly about buying a gun.
I was delighted, though, when the plants did indeed re-grow, bushier than ever, protected from hungry beaks. They began flowering early/mid May. This year, rather than leaving them to their own devices, I've been treating them more like tomatoes: cutting off as many tendrils and side shoots as I can, to stimulate better flowering and vertical growth.
It's time-consuming but satisfying, since this method really seems to work. The more I cut, the more they grow and flower.
Here are my top sweetpeas from this year, by fragrance & colour.

This creamy-white flower has an unusual, subtle scent, somewhere between almonds and lemons. I adore it. Not prolific, but I have to rank it #1 on scent alone. One to grow again next year.
2. 'Barry Dare' and 'Prince Edward of York'
Both of these have vivid, attractive pink flowers and a light rose scent. Less prolific than 'Matucana,' so next year I'll grow more of them.

A bi-colour purple and magenta flower, it's vigorous and incredibly prolific.
The scent is strong, with a slight lemon undertone. Overall a great choice for adding colour and fragrance to a bouquet, or simply, as in this picture, gathering in one vase. Definitely one to grow again.

I'd probably include two cultivars in this list: 'Lord Nelson and 'Black Knight.'
'Lord Nelson' flowers are a striking, unusual shade of blue, akin to a royal navy. It's very attractive, but, contrary to seed packet claims, I have found it has virtually no scent.
Also on this list is 'Black Knight'. The flowers are an intense dark maroon. It is vigorous and a prolific flowerer. It lacks impact on its own or amongst other purple tones, but is good amongst a pink and white bouquet. However, as it has no scent, I won't be selecting it again.
Any suggestions for good scented cultivars, please let me know...