Can you recommend some fast growing climbers to cover fence

Clematis armandii ..... EVERGREEN CLEMATIS

White blooms in late winter and early spring. Grows 25’ by 6-10’. Zone 7-9. Vigorous evergreen, early-flowering climber from China. Deep green leaves have 3 leaflets with marked veining. The fragrant white flowers are large (21⁄2”) and saucer-shaped and appear in late winter and early spring. Well-drained soil is a must!

Passion Flowers and Passion Fruit

Passion flowers (Passiflora spp.) are perennial woody vines, mostly from tropical America but with a few species originating in Asia, Australasia and the Polynesian Islands. They climb through the supporting vegetation by means of coiled tendrils. Many of them have showy fragrant flowers and several produce edible fruits.

both would need to be planted in the ground for best results. Clematis liked to be planted deeply and prefer to have their lower growth in the shade.

Lift enough of the slabs to dig hole 4 x size of the pot your plant comes in, add new compost to approx half the hole mix with the dug out soil water really well then plant whichever you choose. The passion flower grows approx 30ft and the clematis not far short

Inthe ground for climbers would be best. Have a look at Trachleospermum jasminoides - the Clematis armandii above has a nasty habit of having all its growth at the top with bare stems below, and when it flowers, its so early you're not outside much anyway. Eccremocarpus scaber is good - supposed to be an annual (in cold areas it probably would be) but in a sheltered spot, I've had it evergreen all winter and in full flower by end April - and it flowers right throughout the summer.Also the classic Jasmine nudiflorum worth considering; will need support, as will all the climbers mentioned - either wires across the wall, trellis, or for clematis, the easiest option is clematis netting. And the hybrid clematis, of course, like Hagley hybrid, Niobe, hundreds to choose from., tho all deciduous.
When you lift a couple of slabs, dig as mentioned above, but add fish, blood and bone to the soil, some chicken manure pellets, and if you're planting now, some Growmore, but do that next Spring if not. Addition of organic soil conditioning compost would be useful too.
A word of caution - there are rapid growing climbers, but they will get out of hand rapidly too, and you'll need a machete every few months!

If you really want rapid cover, I recommend you grow Tropaeleum peregrinum, the Canary Creeper, and Eccremocarpus, from seed - they'll both be 8/10 feet high in a season. Get the seeds early next year and start them off inside, or wait till April and put straight in the ground. The Canary creeper will die off in the winter, but you'll have a summer of cover and flowers.