Biggs laughingly called the tree felling "the nightmare on Royal Hospital Way".
Titchmarsh replied: "I was not solely responsible for the removal of the trees but a view of a grade one listed building by Sir Christopher Wren is rather better than overgrown shrubs and trees.He added: "It was not my idea. This is important lest I read it in the Sun newspaper tomorrow. I am part of a board of commissioners. I finish in March having been on for six years. I was presenting Chelsea at the time I was appointed and my link with the RHS made me another skill set if you like."
He said: "The overgrown shubbery at the Royal Hospital which was just that, a Victorian shubbery masking from view the Sir Christopher Wren view and that it really disturbed something important, its grandeur and its scale, which is what we've done."
He added: "There was quite a lot of local opposition because people do not like trees being chopped down particularly and quite right too. You need people to look at their own back yards and take stewardship of it.
"The decision was not just by me but I was on the board that did recommend it. I hope that the show will benefit."
Last year, Chris Sumner of the Garden History Society said the new landscaping by George Carter was "neo- baroque, but too stripped down [and] takes out much later planting, even some good specimen trees which soften the view towards developments on the far side of the river."
Biggs defended the Austrlian ANZAC commemorative knitted poppy display, saying it was not a pale imitation of the Tower of London poppies in 2014.
She said: "Referring to the ceramic poppies at the Tower of London, they were very different things. They were for sale, they were an amazing installation, that was an artist creating them and they're beautiful. These poppies evolved out of two ladies in Australia and that was an amazing story when [designer] Philip [Johnson] came through to us and said are you aware of this amazing story, so yes both stories are poppies but the stories they tell are very different though they are two amazing stories very close to each other in years".
The scheme is part of £1.3m of work and allows two more show gardens to be built at that site, as well as Johnson's poppy show feature.
Titchmarsh was involved in the initial design phase as a commissioner of the hospital.
The project involved restoration of South Terrace to its original C17th design intention, removal of trees and shrubs along the southern boundary, regrading and relaying of paths and terraces; introduction of formal soft landscape elements, repair of steps, repainting of railings and gates. Introduction of pedestrian gate either side of double gate for maintenance only on southern boundary, replacing below ground cisterns for water storage, and removal of external access stair to south-east facade of the Royal Hospital.
Screening shall be in place for the extent of the Chelsea Flower Show to mask the back of trade stands.
Designer is George Carter and contractor is Willerby.
The scheme is being paid for from funds ring-fenced for the renovation of hospital buildings and grounds, that were generated by the sale of the lease of a property on the Royal Hospital Chelsea site.
A RHC representative said: "It therefore has not impinged on the RHC’s daily running costs to offer a home and care to the Chelsea Pensioners."Carter developed the plans for the Royal Hospital’s South Terrace to once again ‘act as a plinth’ on which the Grade I listings buildings are set, opening up views of the 300-year-old heritage site.
The work involves redeveloping the South Terrace and an area of the gardens to allow the buildings to have clear and open views both to and from the banks of the River Thames, as Wren originally intended. Unsympathetic landscaping during the 19th Century caused views of the Royal Hospital to be obstructed for several decades, and its redesign forms just one part of a renovation programme of the Royal Hospital’s estate that has included the refurbishment of the Long Wards housing the Chelsea Pensioners, which were completed in October 2015."
Paul Hatt, secretary and acting chief executive officer of the Royal Hospital, said: "We are very pleased with the support our application has received from many eminent UK conservation bodies and of course RBK&C planning and conservation officers and councillors and our most knowledgeable Commissioner on this topic, Alan Titchmarsh.
"We are required to protect and preserve the historic nature and fabric of the site, and we are convinced that this scheme will restore the setting of this important heritage site for future generations."In addition to the landscaping alterations, the Royal Hospital will change the paths on the South Terrace to sealed gravel to ensure that all areas of the grounds are accessible to Chelsea Pensioners (including those using mobility scooters or wheelchairs).