Leaf size and shape is the single biggest tell for this genus — get that right and you've almost certainly got the right group.
1
Look closely at the leaves: are they tiny, scale-like, pressed flat against the stem almost like a miniature conifer (or small, under about 2cm, narrow and densely packed)?
No — normal broad oval leaves, 2.5cm or longer, glossy→ question 2
2
Confirm with overall size and habit: is it a low, dense mound or mat under about 60cm and wider than it is tall, or a taller, more upright bushy plant from 60cm up to 1.5m or more?
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If you are still unsure
If you genuinely can't tell which type you have, treat it as the tender tender_large_leaved group for winter protection — move a potted plant somewhere sheltered, or fleece it in open ground before a hard frost. Over-protecting a genuinely hardy plant costs a little effort; leaving a tender one exposed can kill it outright.
COMMON MISTAKE
Assuming a hebe with broad, glossy leaves is just as hardy and wind-tolerant as the small-leaved alpine/whipcord types, because both are described as 'hebes' and both tolerate coastal wind well. Large-leaved hybrids are usually noticeably less cold-hardy than the small-leaved types and need moving under cover or fleecing in a hard winter that the small-leaved types shrug off outdoors unprotected.
Already know the variety name?
The name on the label tells you the type.
Hebe pinguifolia ‘Pagei’Hardy alpine/whipcord hebe › · Small oblong silvery-grey leaves, white flowers, dense mat 10-50cm tall but spreading to 1m.
Hebe cupressoides ‘Boughton Dome’Hardy alpine/whipcord hebe › · Tiny grey-green cypress-like scale leaves, pale lilac flowers, dense neat dome to 45cm.
Hebe ochracea ‘James Stirling’Hardy alpine/whipcord hebe › · True whipcord type, scale leaves that turn a distinctive burnt-gold colour in winter, white flowers.
Hebe rakaiensisHardy alpine/whipcord hebe › · Small apple-green leaves, white flowers, neat rounded dome, one of the most widely planted hardy hebes.
Hebe albicans ‘Pink Elephant’Hardy alpine/whipcord hebe › · Compact grey-green leaves edged pink and cream — the leaf colour alone is a strong identifier.
Hebe albicans ‘Red Edge’Hardy alpine/whipcord hebe › · Small grey-green leaves with a fine red margin, white flowers ageing lilac.
Veronica lycopodioidesHardy alpine/whipcord hebe › · True whipcord hebe (sold under both Veronica and Hebe), tiny yellow-green scale leaves, sparse white flowers — 'often shy to flower' by its own reputation.
Hebe topiariaHardy alpine/whipcord hebe › · Small grey-green leaves in a neat dome shape, one of the most commonly sold compact hebes at UK garden centres.
Hebe ‘Great Orme’Tender large-leaved hebe › · Narrow but full-sized dark green leaves, pink flower spikes fading to white, upright 1-1.5m.
Hebe ‘Midsummer Beauty’Tender large-leaved hebe › · Long narrow purple-tinged young leaves, lilac-mauve flower spikes fading white, one of the largest hebes at 1.5-2.5m.
Hebe speciosaTender large-leaved hebe › · Large glossy fleshy leaves, deep pink-red/purple flowers to 8cm — the parent species behind many of the large-leaved hybrids, among the least hardy.
Hebe speciosa ‘La Séduisante’Tender large-leaved hebe › · Broad glossy dark green leaves (purple beneath when young), reddish-purple flowers — RHS-rated H3, best in mild/coastal gardens or a pot brought under cover.
Hebe ‘Amy’Tender large-leaved hebe › · Glossy dark green leaves tinted purple in cold weather, large purple flower spikes.
Hebe ‘Marjorie’Tender large-leaved hebe › · Elliptic glossy green leaves, pale violet flowers fading white, one of the more compact large-leaved hybrids at 0.5-1m.
Hebe ‘Autumn Glory’Tender large-leaved hebe › · Leaves edged purple-red, purple-blue flowers with an unusually long season into early winter.
Hebe ‘Alicia Amherst’Tender large-leaved hebe › · Glossy dark green leaves that bronze in cold weather, royal purple flower spikes.